Inorganic bonded devices and structures

ABSTRACT

An inorganic coating may be applied to bond optically scattering particles or components. Optically scattering particles bonded via the inorganic coating may form a three dimensional film which can receive a light emission, convert, and emit the light emission with one or more changed properties. The inorganic coating may be deposited using a low-pressure deposition technique such as an atomic layer deposition (ALD) technique. Two or more components, such as an LED and a ceramic phosphor layer may be bonded together by depositing an inorganic coating using the ALD technique.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Nonprovisional patentapplication Ser. No. 15/802,273 filed Nov. 2, 2017, which claims benefitof U.S. Provisional Patent Application No. 62/417,262 filed Nov. 3, 2016and U.S. Provisional Patent Application No. 62/417,237 filed Nov. 3,2016, the contents all of which are incorporated by reference herein intheir entirety.

BACKGROUND

Luminescent particles or layers in a semiconductor device that aredeposited or bonded using traditional techniques, for example withsilicone, may suffer from a shorter life span due to degradation of theorganic binder. Even in a more costly processes where luminescentparticles sintered together at high temperature to form a ceramic or areincorporated into a glass, the resulting wavelength converting plate istypically attached to a semiconductor device with an organic glue thatmay degrade and discolor under operation at high temperature and highflux densities of short wavelength light, for example blue or UV. As aresult, devices with luminescent particles deposited or bonded usingtraditional techniques may need to be replaced on a less than ideal timecycle. Additionally substrates, other than semiconductor devices, bondedusing traditional techniques may also experience these unwanted effects.Accordingly, such techniques are deficient when it comes to bondingluminescent particles and/or ceramic layers to devices and othersubstrates.

SUMMARY

In accordance with aspects of the invention, a plurality of opticallyscattering and/or luminescent particles may be deposited onto acomponent. An inorganic coating may be deposited onto the plurality ofoptically scattering particles using a low-pressure depositiontechnique. The plurality of optically scattering particles may be bondedtogether to form a three-dimensional film, such that an opticallyscattering and/or luminescent particle is bonded to another opticallyscattering particle and/or luminescent by the inorganic coating. Theinorganic coating may comprise multiple layers and one or more of thelayers may be an oxide coating and the optically scattering and/orluminescent particles may be deposited using a technique such assedimentation, electrophoretic deposition (EPD), stenciling, ordispensing. The optically scattering particles and/or luminescent may bephosphor particles and the component may be a metal, a substrate, aceramic, a semiconductor, an insulator, or a light emitting device, forexample a light emitting diode (LED) or laser. The low-pressuredeposition technique may be an atomic layer deposition (ALD) technique.The component may be removed or partially removed to allow thethree-dimensional film to receive a photoexcitation at one surface andemit a light from the opposite surface. The component may also betransparent to the light emission and not removed. The component mayalso be thermally conductive. The component may also be opaque to thelight emission, may be reflective and photoexcitation may be received onthe same surface that light is emitted. The component itself may be thesource of excitation such as a LED or laser. The inorganic coating'scoefficient of thermal expansion (CTE) may be substantially matched tothe CTE of the plurality of optically scattering particles or to the CTEof the component. The inorganic coating's index of refraction may besubstantially matched to the index of refraction of the plurality ofoptically scattering particles or to the index of refraction of thecomponent.

In accordance with an implementation, a three-dimensional film mayreceive a light of a first wavelength. The three-dimensional film mayabsorb or partially absorb this light and emit a light of a secondwavelength. The light emitted may be the second wavelength or acombination of first and second wavelength.

In accordance with an implementation, multiple three-dimensional filmsmay be configured to be adjacent to each other, for example in a linearor matrix array, such that a separation layer, such as an absorbingmaterial or a reflective material, is located between the adjacentthree-dimensional films. The multiple three-dimensional films may beplaced on top of individual light emitting components that can, forexample be individually activated, such that each three-dimensional filmis configured to produce a light emission independent of or isolatedfrom each other with reduced cross talk for example. Alternatively, thelight emitting pixels can be excited from a rastered light source suchas a laser or electron beam. Such an arrangement may be used in systemssuch as automotive lighting, for example adaptive front lighting system(AFS), camera flash, displays, or the like.

In accordance with another implementation, a surface of a componentand/or ceramic phosphor layer may be roughened or by having groves addedto a surface. An inorganic coating may be deposited onto the roughenedor trenched surfaces using a low-pressure deposition technique bindingthe two components together with the inorganic coating.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosed subject matter, are incorporated in andconstitute a part of this specification. The drawings also illustrateimplementations of the disclosed subject matter and together with thedetailed description serve to explain the principles of implementationsof the disclosed subject matter. No attempt is made to show structuraldetails in more detail than may be necessary for a fundamentalunderstanding of the disclosed subject matter and various ways in whichit may be practiced.

FIG. 1a shows a cross-sectional view of light being absorbed and emittedby a three dimensional film with an off axis excitation;

FIG. 1b shows a cross-sectional view of light being emitted by a lightemitting device and absorbed and converted through a three dimensionalfilm;

FIG. 1c shows a cross-sectional view of light being absorbed andconverted through a three dimensional film;

FIG. 1d shows a cross-sectional view of light being absorbed andconverted through a three-dimensional film surrounded, in part, byspacer material;

FIG. 2 shows a top sectional view of an arrangement of three-dimensionalfilms;

FIG. 3 shows two components bonded via an inorganic coating;

FIG. 4 schematically depicts a lighting device;

FIG. 5a schematically depicts luminescent powder particles having asol-gel first coating;

FIG. 5b schematically depicts an aspect of a particulate luminescentmaterial;

FIG. 5c schematically depicts an aspect of a particulate luminescentmaterial;

FIG. 5d schematically depicts an aspect of a particulate luminescentmaterial;

FIG. 6a shows the relative light output (LO) as a function ofdegradation time (in hours) for phosphor powder before (SiO₂ only) andafter ALD coating (Al₂O₃ on SiO₂); degradation conditions: 60° C./100%relative humidity: ALD-1: 20 nm Al₂O₃ on phosphor; ALD-2: 40 nm Al₂O₃ onphosphor; ALD-3: 20 nm Al₂O₃ deposited on SiO₂ coating; SiO₂-1: sol-gelSiO₂ coating on phosphor (basis of ALD-3);

FIG. 6b shows the relative light output (LO) as a function ofdegradation time given in hours (85° C./100% RH); ALD-3: 20 nm Al₂O₃ onSiO₂ coating; ALD-4: 20 nm Al₂O₃/Ta₂O₅ nanolaminate; deposited on thinSiO₂ layer (<10 nm); ALD-5: 20 nm Al₂O₃/Ta₂O₅ nanolaminate; deposited onSiO₂ coating; ALD-6: 20 nm Al₂O₃/HfO₂ nanolaminate; deposited on SiO₂coating; and

FIG. 6c shows the relative light output (LO) as a function ofdegradation time given in hours (85° C./100% RH); ALD-3 and ALD-6samples as described above; ALD-7: 20 nm Al₂O₃/HfO₂ nanolaminate on thinSiO₂ layer (<10 nm), nanolaminate design: 4×[1.5 nm Al₂O₃/3.5 nm HfO₂];ALD-8: 10 nm Al₂O₃/HfO₂ nanolaminate on thin SiO₂ layer (<10 nm),nanolaminate design: 2×[1.5 nm Al₂O₃/3.5 nm HfO₂]. The sol-gel SiO₂coatings in general have a layer thickness in the range of 150-200 nm,unless indicated otherwise. The thin SiO₂ layers, indicated withthicknesses <10 nm in general will have a mean layer thickness in therange of about 1-10 nm.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An inorganic coating can be used as a bonding mechanism and may be usedto bond particles together to create three dimensional films that mayhave some degree of porosity depending on the packing density of theparticles and the degree of gap filling, to bond particles to acomponent, including a light emitter, to bond a component to anothercomponent, or for like purposes. The inorganic coating may providebenefits, over alternatives, such as improved reliability, decreasedcost, generation of a transparent or semi-transparent film, coefficientof thermal expansion (CTE) matching, index of refraction, or the like.Particles coated with inorganic material may experience additionalbenefits such as a higher resistance to moisture.

According to implementations of the disclosed subject matter, opticallyscattering particles (also including and referred to as luminescentparticles herein) can be bonded together via an inorganic coatingapplied using a low-pressure deposition technique to create a threedimensional film. The porous three-dimensional film may be a scatteringfilm and may be freestanding or bonded to a component such as asubstrate, a light emitting device, ceramic phosphor, or the like.Excitation including photoexcitation, such as from an LED or laser maybe used to excite all or a portion of the three dimensional film. Otherforms of excitation may include cathodoluminescence from an electronbeam source, radioluminescence from an X-ray source, orelectroluminescence from an applied electromagnetic field. As a result,a converted emission may exit the three-dimensional film from the sameside that the excitation entered or from a different side than fromwhich the excitation entered. The emitted light may be the convertedemission or a combination of the converted emission and photoexcitationlight where, preferably, the emitted light has a desired correlatedcolor temperature (CCT) with a particular color-rendering index (Ra).Further, the light photoexcitation entering the three-dimensional filmmay experience a scattering effect due to interaction with portions ofthe three-dimensional film.

According to implementations of the disclosed subject matter, aplurality of optically scattering particles may be bonded via aninorganic coating applied to the particles or agglomeration ofparticles. The particles may be composed of one or more applicableluminescent or optically scattering material such as phosphor particleswith or without activation from rare earth ions, aluminum nitride,aluminum oxynitride (AlON), barium sulfate, barium titanate, calciumtitanate, cubic zirconia, diamond, gadolinium gallium garnet (GGG), leadlanthanum zirconate titanate (PLZT), lead zirconate titanate (PZT),sapphire, silicon aluminum oxynitride (SiAlON), silicon carbide, siliconoxynitride (SiON), strontium titanate, titanium oxide, yttrium aluminumgarnet (YAG), zinc selenide, zinc sulfide, and zinc telluride, diamond,silicon carbide (SiC), single crystal aluminum nitride (AlN), galliumnitride (GaN), or aluminum gallium nitride (AlGaN) or any transparent,translucent, or scattering ceramic, optical glass, high index glass,sapphire, alumina, III-V semiconductors such as gallium phosphide, II-VIsemiconductors such as zinc sulfide, zinc selenide, and zinc telluride,group IV semiconductors and compounds, metal oxides, metal fluorides, anoxide of any of the following: aluminum, antimony, arsenic, bismuth,calcium, copper, gallium, germanium, lanthanum, lead, niobium,phosphorus, tellurium, thallium, titanium, tungsten, zinc, or zirconium,polycrystalline aluminum oxide (transparent alumina), aluminumoxynitride (AlON), cubic zirconia (CZ), gadolinium gallium garnet (GGG),gallium phosphide (GaP), lead zirconate titanate (PZT), silicon aluminumoxynitride (SiAlON), silicon carbide (SiC), silicon oxynitride (SiON),strontium titanate, yttrium aluminum garnet (YAG), zinc sulfide (ZnS),spinel, Schott glass LaFN21, LaSFN35, LaF2, LaF3, LaF10, NZK7, NLAF21,LaSFN18, SF59, or LaSF3, Ohara glass SLAM60 or SLAH51, and may comprisenitride luminescent material, garnet luminescent material, orthosilicateluminescent material, SiAlON luminescent material, aluminate luminescentmaterial, oxynitride luminescent material, halogenide luminescentmaterial, oxyhalogenide luminescent material, sulfide luminescentmaterial and/or oxysulfide luminescent material, and luminescent quantumdots comprising core materials chosen from cadmium sulfide, cadmiumselenide, zinc sulfide, zinc selenide, and may be chosen formSrLiAl₃N₄:Eu (II) (strontium-lithium-aluminum nitride: europium (II))class, or any combination thereof.

The size of the luminescent or optically scattering particles may dependon the application of the particles in a light emitting or like system.The size may be between a nanometer to 100 μm D₅₀ or between 1 μm and 50μm D₅₀ or 3 μm to 30 μm D₅₀ or 5 μm to 25 μm D₅₀ or 7 μm to 20 μm D₅₀.Here, D represents the diameter of powder particles, and D₅₀ means acumulative 50% point of diameter (or 50% pass particle size) and mayalso be referred to as an average particle size or median diameter. Nanosized to 5 μm phosphor particles can be suitable for micro LED pixelcoverage, whereas 5 to 25 μm particle sizes are more suitable for ahigher power LED having a millimeter square area or more.

According to implementations of the disclosed subject matter, aplurality of optically scattering particles may be deposited onto acomponent. The component may be composed of one or more applicablematerial such as diamond, silicon carbide (SiC), single crystal aluminumnitride (AlN), gallium nitride (GaN), or aluminum gallium nitride(AlGaN), aluminum indium gallium nitride (AlInGaN), optical glass, highindex glass, sapphire, diamond, silicon carbide, alumina, III-Vsemiconductors such as gallium phosphide, II-VI semiconductors such aszinc sulfide, zinc selenide, and zinc telluride, group IV semiconductorsand compounds, metal oxides, metal fluorides, an oxide of any of thefollowing: aluminum, antimony, arsenic, bismuth, calcium, copper,gallium, germanium, lanthanum, lead, niobium, phosphorus, tellurium,thallium, titanium, tungsten, zinc, or zirconium, polycrystallinealuminum oxide (transparent alumina), aluminum oxynitride (AlON), cubiczirconia (CZ), gadolinium gallium garnet (GGG), gallium phosphide (GaP),lead lanthanum zirconate titanate (PLZT), lead zirconate titanate (PZT),silicon aluminum oxynitride (SiAlON), silicon carbide (SiC), siliconoxynitride (SiON), strontium titanate, yttrium aluminum garnet (YAG),zinc sulfide (ZnS), spinel, Schott glass LaFN21, LaSFN35, LaF2, LaF3,LaF10, NZK7, NLAF21, LaSFN18, SF59, or LaSF3, Ohara glass SLAM60 orSLAH51, or any combination thereof, aluminum oxynitride (AlON),polycrystalline alumina oxide (transparent alumina), aluminum nitride,cubic zirconia, diamond, gallium nitride, gallium phosphide, sapphire,silicon carbide, silicon aluminum oxynitride (SiAlON), siliconoxynitride (SiON), spinel, zinc sulfide, or an oxide of tellurium, lead,tungsten, or zinc. The component may be any applicable component such asa metal, a substrate, a ceramic, a semiconductor, a light emittingdevice, an insulator, or the like.

The particles may be deposited using any applicable technique such assedimentation, EPD, stenciling, dispensing in a volatile medium, or thelike.

According to implementations of the disclosed subject matter, aninorganic coating may be applied to the plurality of opticallyscattering particles. The coating material may be selected from the samelist of materials that may make up the optically scattering particles orsubstrates, or other applicable materials such as aluminum oxide Al₂O₃,hafnium oxide HfO₂, tantalum oxide Ta₂O₅, titanium oxide TiO₂, zirconiumoxide ZrO₂, another transparent oxide, or the like. The coating may besingle layered or be multi layered of the same or different material,and may be applied by depositing a material at the particle surface bydeposition from the gas phase, such as via an atomic layer deposition(ALD) process. Atomic layer deposition could be a suitable method todeposit thin, conformal coatings of various inorganic materials onpowder particles. For instance, methods may be used to fluidizeparticles during the ALD coating process to improve the coating qualityby preventing particle-particle agglomeration that leads to decreasedcoating quality.

The coating may be an oxide, nitride, carbide, arsenide, phosphide,fluoride, sulfide, selenide, telluride, metal, single element, ortellurite glass. The coating may be any of the materials or combinationof materials listed for the particles or substrates. The thickness ofthe inorganic coating may be determined, at least in part, by the sizeof optically scattering particles bonded by the inorganic coating.Larger particles require a thicker inorganic coating and, accordingly,smaller particles may result in a thinner inorganic coating. Accordingto implementations, the inorganic coating may be as thin as a singlemonolayer of around 3 Angstroms to as thick as 1000 Angstroms that is1/10th of a micron, be between 1/10th of a micron to 1 micron, or bebetween 1 micron and 10 microns, or the like.

The plurality of optically scattering particles 131 may be bondedtogether by the inorganic coating 132 deposited onto the plurality ofparticles as shown in FIGS. 1a-1d . The particles may be bonded using alow pressure or low partial pressure deposition where coating materialshave a large diffusion length that penetrate deeply, such as CVD, lowpressure CVD, ALD, or the like. The inorganic coating may create a bondthat binds the plurality of particles together in either a freestandingthree-dimensional film or over a component such as a substrate or LED.The inorganic coating may also bind the three-dimensional particle filmto the component such as a substrate or LED.

As shown in FIG. 1b , the optically scattering particles 131 bondedtogether via the inorganic coating 132 to produce a three dimensionalfilm 125 may be over an LED 160. The LED 160 may emit a light 171 a and171 b from a light emitting layer or region 161 which traverses throughthe three dimensional film 125 and exits from the surface opposite tothe LED 160. As shown via the distinctive arrows, a portion of the lightemitted by the LED 160, 171 a, may be absorbed by a optically scatteringparticle 131 and a portion of the light, 171 b may pass through thethree dimensional film 125 without being absorbed by an opticallyscattering particle. Light 171 a, which is absorbed by a luminescentscattering particle 131, may be converted to a different wavelengthlight by the luminescent particle or phosphor. A converted light 170 cmay exit the three dimensional film 125 such that the light 170 c iscombined with the light 171 b to form the device emission, and thecombined light is the desired light emission from the three dimensionalfilm 125. For example, some of blue light emitted by the LED may beconverted to yellow and the combined blue and yellow light make a lightthat appears white. An additional phosphor that converts to the red maybe added for a warmer white (lower CCT) and better color rendering(higher Ra). Alternatively, an UV LED could be used with a blue andyellow phosphor, where the UV is fully absorbed. Also, a third redphosphor could be added for a warmer white and better color rendition.An amber LED device may be created by using an amber phosphor with blueor UV LED for full wavelength conversion to an amber emission.

According to an implementation, a portion of the inorganic coating maybe in contact with a particle A and a particle B such that it both coatsthe two particles A and B and also bonds them together. Alternatively,according to implementations of the disclosed subject matter, a portionof the three-dimensional film may rest on a component including asubstrate while another portion of the film is freestanding. Thefreestanding portion of the film may allow light excitation to enterfrom one side and an emission to escape from another side. For exampleon a substrate with multiple areas removed and a freestanding portion ofthe film bridging the gapped area, an array of pixels may be formed. Inan illustrative example, as shown in FIG. 1c , a portion of thesubstrate 135 may be removed to create a gap, 165. The three-dimensionalfilm 125 may rest on the remaining portions of substrate 135. A lightexcitation 185 may be sent towards the three-dimensional film from alight-emitting device located on one side of the substrate. The lightexcitation 185 may be absorbed, at least in part, by the bondedparticles 131 of three-dimensional film 125 and a light emission 180 mayescape the three-dimensional film 125 from a side opposite from the sidewhere the light excitation 185 entered the three-dimensional film 125.The substrate may be thermally conductive and reflective, such as ametal for example silver or aluminum, or a diffuse reflective material,such as boron nitride. Alternatively the substrate may be a thermallyconductive and absorptive material, such as pyrolytic graphite. Havingeither a reflective or absorptive substrate with good thermalconductivity may be useful in reducing cross talk between pixels in araster scanned laser system having high optical power densities.Alternatively as depicted in FIG. 1d the optically scatteringparticles/luminescent particles can be deposited in recesses 137 of asubstrate 136 with 135 and, optionally, at least a portion of theopposite side of the substrate 135 can be removed to expose thethree-dimensional film for transmitting the radiation, otherwise in theformer case excitation radiation may be introduced on the same side. Forthis case the material of the substrate 136 or spacer or separationmaterial 136 attached to 135 may be reflective or absorptive and thesubstrate 135 or spacer material attached to substrate 135 may bereflective or absorptive. The material 136 and 135 may be the same withrecess or cavity 137 formed in it, for example 135/136 may be a siliconwafer with recesses 137 etched in it. Alternatively, 136 can be anadditional layer of the same or different material on 135. For example,substrate 135 can be boron nitride with a spacer or separation material136 being a layer of pyrolytic graphite having recesses or cavities 137formed before or after placement on substrate 135.

It will be understood by one skilled in the art that opticallyscattering particles may be disposed on a component prior to beingbonded via an inorganic coating, as provided in the implementations thusfar, or may be bonded via an inorganic coating and then deposited onto acomponent. In another embodiment, the particles can be coated first andthen be bonded together in aggregate. This can be done with a subsequentALD coating or if the original coating has a low enough softeningtemperature, a thermal treatment may bind the coated particles together.

A three-dimensional film may be configured to receive a light of a firstwavelength. As a result of the absorption of this excitation light byone or more optically scattering/luminescent particles, portions of thereceived light may be converted to a different light with a secondwavelength. Depending on the characteristics of the three-dimensionalfilm or the particles, or both, the light emission may contain light ofthe second wavelength or light that is a combination of the firstwavelength (e.g., where the original light may not have been absorbed bya particle in the three-dimensional film and passed or reflected throughthe film) and the second wavelength. As an example, a three-dimensionalfilm may receive a blue light and the three-dimensional film may convertpart of the blue light to emit a yellow light. The overall lightemission through the three-dimensional film may be a combination of theblue light and converted yellow light, providing an effective whitelight as a result.

The coefficient of thermal expansion (CTE) of the coating may be nearlymatched to that of the optically scattering particles. Alternatively orin addition, the CTE of the coating may be nearly matched to that of thecomponent on which the particles are disposed or with which an inorganiccoating is used to form a bond to the three dimensional film or othercomponent, as disclosed herein.

The index of refraction of the coating may be nearly matched to that ofthe optically scattering or luminescent particles. Alternatively or inaddition, the index of refraction of the coating may be nearly matchedto that of the index of refraction of a transparent component on whichthe particles are disposed or with which an inorganic coating is used toform a bond to the three dimensional film or other component, asdisclosed herein. Alternatively, the index of refraction of the coatingmay be lower than that of the optically scattering or luminescentparticles. In this case the individual particles in the agglomerateretain some of their scattering properties. If the index of refractionof the coating matches the particles than the scattering of theindividual particles is lost and the scattering properties of the porousthree-dimensional film becomes the prominent scattering mechanism. Ifmultiple particle materials are used such as a garnet phosphor and anitridosilicate phosphor, the index of refraction of the coating maymatch the index of refraction of the garnet, but the nitridosilicatephosphor may still scatter because of its higher index of refraction.For example an alumina coating will have an index of refraction that isnearly matched to a garnet phosphor (green or yellow) at around 1.8,whereas the index of refraction of the nitridosilicate phosphor (red) isaround 2.2.

According to an implementation of the disclosed subject matter, multiplethree-dimensional films may be arranged adjacent to each other such thata spacer or separation layer separates each pixel. The separation layermay be, for example, an absorptive layer or a reflective layer and maybe configured for high contrast with low cross talk and high efficiency.An absorptive layer may be composed of any applicable absorptivematerial such as silicon or pyrolytic graphite and a reflective layermay be any applicable reflective material such as specular silver,diffusive reflective boron nitride, a loaded silicone with for exampleTiO₂, an epoxy molding compound, or other white molding compounds. As anexample, as shown in FIG. 2, multiple three-dimensional films 230 may bearranged in a matrix or pixelated pattern 210. A reflective orabsorptive layer 220 may separate each film that can also be the spaceror substrate in cross sectional FIG. 1d . The reflective or absorptivelayer may serve to keep light emitted by the multiple three-dimensionalfilms separate from each other and to visually maintain the pixelatedpattern with reduced cross talk. According to an implementation,multiple light emitting devices may be placed underneath the multiplethree-dimensional films that are separated by a separation layer. Themultiple devices may be individually addressable and emit light towardsone or more specific pixel films when activated such that the lightemission through the one or more three-dimensional films can be moredistinctly controlled. As an example, an automotive headlight maycontain multiple LEDs disposed underneath a pixel-patterned group ofthree-dimensional films, which are separated from each other by aseparation material. The matrix may contain 2, 3, 5, 10 s, to 100 s ofpixels for a camera flash. The matrix may contain, for example, 1000,5000, or 10000 pixels for an automotive adaptive front lighting system(AFS) and many times this number for a display. Where millions of pixelsare required for an application, a raster scanned laser may be used.Raster scanning may be accomplished with a microelectromechanical system(MEMS) based mirror or with an acousto-optic reflector or deflector. AFScan be used to level the beam of a headlamp when a vehicle is heavilyloaded, climbing or descending a hill or valley, traversing a rough orundulating road, steering the beam around curves and turns, creating aprojection pattern that creates a hole in illumination so that driversof oncoming vehicles and vehicles ahead traveling in the same directionare not blinded or dazzled. U.S. Pat. Nos. 6,406,172 and 7,566,155 arehereby incorporated herein, in their entirety, by reference. Forexample, the left column of three-dimensional films and the respectiveLEDs beneath them may default to being off. Upon receiving a signal thatthe steering wheel of the automobile is turned by over 30% of its travelcounter clockwise, the LEDs beneath the left column of three-dimensionalfilms may be switched to on, and emit a light towards the left column ofthree-dimensional films. The left column of three-dimensional films mayreceive the light excitation and emit a light from the headlight of theautomobile such that the emitted light illuminates a scene further leftthan the scene originally illuminated by the headlight before the 30%counterclockwise travel of steering wheel turn was reached. An advantageof using such an arrangement is that the headlight need not containmoving components to provide turn-based illumination. AFS systems may befar more complex than the simple system described above and employcameras, light detection and ranging (LiDAR), image processors, andcontrollers. Infrared (IR) LEDs or vertical cavity surface emittinglasers (VCSELs) may provide supplemental light and information to thesensors and detectors. Such systems of image detection and processingcan anticipate road topology, sense vehicle and pedestrian traffic toprovide optimal lighting for the vehicle driver. Vehicle to vehicle,infrastructure, pedestrian, target, or object (V2X) communications maybe used to provide position, speed, vehicle type and dimensions, etc. toadaptive front, rear, and side exterior lighting systems. A componentwith a desired thermal conductivity, for example, diamond, copper,silver, or a combination thereof, may be used as a heat sink. In theexample provided herein, a substrate with a desirable thermalconductivity may be used as a heat sink in an automotive laser headlampor other adaptive lighting system as the opticallyscattering/luminescent particles, such as phosphor, may be excited athigh power densities by the laser beam, creating a need for a heat sink.Secondary optics such as a parabolic reflector and imaging lens may beemployed. The matrix or pixelated light source may lie on a reflectiveplanar surface with a half parabolic reflector overlaying the reflectiveplanar surface with an imaging or projector lens in the reflected lightoptical path.

According to implementations of the disclosed subject matter, areflective coating may be in contact with or in the optical path of oneor more sides of a three-dimensional film. As an example, a reflectiveand thermally conductive mirror could be disposed between thethree-dimensional film and a substrate. As shown in FIG. 1a , a light140 may be emitted towards a three-dimensional film 125, which includesbonded phosphor particles 131. The wavelength of at least a portion ofthe light may be converted within the three-dimensional film 125 and thelight may reach a reflective layer 115, which is disposed over the topof substrate 135. The light may reflect off the reflective layer 115 andexit the three-dimensional film from the same side it entered from.Similarly, a filter, such as a wavelength selective filter may be incontact with or in the optical path of one or more sides of the threedimensional film. As an example, a filter on the emission exit surfaceor emission side of the three-dimensional film 125 (not shown) may bemore reflective of blue light and more transmissive to longer wavelengthlight such as green, yellow and red light. Based on the desired result,filtering the light using this filter may improve wavelength conversionefficiency. U.S. Pat. No. 9,543,478 is hereby incorporated herein in itsentirety by reference. A reflective coating and/or filter may be adistributed Bragg reflector (DBR) or a dichroic made of alternatinglayers of different index materials such as dielectrics. The reflectivecoating and/or filter may also include a metal layer such as one made atleast in part of silver (Ag) and can include additional metal oxides ordielectrics such as TiW or TiWNx layer. A bandpass filter, for example aneodymium Nd coating may be used. An example of a DBR or dichroic filtermay be alternating layers of Nb₂O₅, SiO₂, TiO₂ and any other suitablematerial. The thickness may be at least 10 nm in some embodiments, nomore than 5 microns thick in some embodiments, at least 1 micron thickin some embodiments and no more than 2 microns thick in someembodiments. The total number of layers may be at least 2 layers in someembodiments, no more than 50 layers in some embodiments, at least 10layers in some embodiments and no more than 30 layers in someembodiments. Each layer may be the same thickness or layers of differentthickness may be used. The filter may be deposited by any suitabletechnique including sputtering, plasma vapor deposition, chemical vapordeposition, and evaporation. The filter may be between the excitationsource and the three-dimensional converter film, on the emission side ofthe three-dimensional converter film if these surfaces are different, oron one or more sides of the three-dimensional converter film. For veryhigh luminance (small etendue) applications the large top and/or bottomareas of the three-dimensional converter film can be pumped with otherun-pumped surfaces having a reflector and emission extracted from one ormore edges.

According to implementations of the disclosed subject matter, aninorganic coating, as described herein, may bond a component to anothercomponent where a component could be a substrate, an LED, a ceramicphosphor, ceramic, metal, insulator, semiconductor, or other lightemitting device, or the like. The surface of one or both of thecomponents that are being bonded may be treated to allow for theinorganic coating precursors to more easily access the bonding area ofthe components. The treatment may be a roughening of the surface of oneor both components that the inorganic coating will bond. Alternativelyor in addition, groves may be added to the surface of one or bothcomponents to enable the inorganic coating to penetrate the surface. Asan example, a ceramic phosphor may be bonded to a light emitter or toanother ceramic phosphor, or to a substrate. The coefficient of thermalexpansion (CTE) of the ceramic phosphor and or index of refraction maybe nearly matched to that of the component being bonded to the ceramicphosphor. Surface roughness and/or groves may be formed on one or moreof the surfaces that will be bonded, to enable the ALD coating topenetrate.

As shown in FIG. 3, a substrate 310 may be bonded to a ceramic phosphorplate 330 via an inorganic coating 320. The two surfaces to be bondedtogether may be treated such that surface 315 corresponding to thesubstrate 310 and surface 335 corresponding to the ceramic phosphorplate 330 may be roughened. The roughened surface may allow theinorganic coating 320 to penetrate the entire respective bondingsurfaces during the ALD process. After the treatment process, theinorganic coating 320 may be applied to the two surfaces 315 and 335 viaa low-pressure deposition technique such as the ALD process. Theinorganic coating then bonds the two surfaces 315 and 335 together,resulting in a structure where substrate 310 is bonded to the ceramicphosphor plate 330 via the inorganic coating.

According to implementations of the disclosed subject matter, a ceramicphosphor plate may be composed of Y₃Al₅Oi₂:Ce³⁺. The ceramic phosphorplate may be an amber to red emitting rare earth metal-activatedoxonitridoalumosilicate of the general formula(Ca_(1−x−y−z)Sr_(x)Ba_(y)Mg_(z))_(1−n)(Al_(1−a+b)B_(a))S_(1−b)N_(3−b)O_(b):RE_(n3)wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, 0≤a≤1, 0≤b≤1 and 0.002≤n≤0.2, and RE may beselected from europium(II) and cerium(III). The phosphor in the ceramicphosphor plate may also be an oxido-nitrido-silicate of general formulaEA_(2−z)Si_(5−a)BaN_(8−a)O_(a):Ln_(z), wherein 0≤z≤1 and 0<a<5,including at least one element EA selected from the group consisting ofMg, Ca, Sr, Ba and Zn and at least one element B selected from the groupconsisting of Al, Ga and In, and being activated by a lanthanide (Ln)selected from the group consisting of cerium, europium, terbium,praseodymium and mixtures thereof.

The ceramic phosphor plate may also be an aluminum garnet phosphors withthe general formula (Lu_(1−x−y−a−b)Y_(x)Gd_(y))₃(Al_(1−z)Ga_(z))₅O₁₂:Ce_(a)Pr_(b), wherein 0<x<1, 0<y<1, 0≤z≤0.1, 0<a≤0.2 and 0≤b≤0.1, suchas Lu₃Al₅O₁₂:Ce³⁺ and Y₃Al₅O₁₂:Ce³⁺, which emits light in theyellow-green range; and(Sr_(1−x−y)Ba_(x)Ca_(y))_(2−z)Si_(5−a)Al_(a)N_(8−a)O_(a):Eu_(z) ²⁺,wherein 0≤a<5, 0≤x≤1, 0≤y≤1, and 0≤z≤1 such as Sr₂Si₅N₈:Eu²⁺, whichemits light in the red range. Other green, yellow and red emittingphosphors may also be suitable, including(Sr_(1−a−b)Ca_(b)Ba_(c))Si_(x)N_(y)O_(z):Eu_(a) ²⁺; (a=0.002-0.2,b=0.0-0.25, c=0.0-0.25, x=1.5-2.5, y=1.5-2.5, z=1.5-2.5) including,Sr₂Si₂N₂O₂:Eu²⁺;(Sr_(1−u−v−x)Mg_(u)Ca_(v)Ba_(x))(Ga_(2−y−z)Al_(y)In_(z)S₄):Eu²⁺including, for example, SrGa₂S₄:Eu²⁺; Sr_(1−x)Ba_(x)SiO₄:Eu²⁺; and(Ca_(1−x)Sr_(x))S:Eu²⁺ wherein 0≤x≤1 including, CaS:Eu²⁺ and SrS:Eu²⁺.Other suitable phosphors include, CaAlSiN₃:Eu²⁺, (Sr,Ca)AlSiN₃:Eu²⁺, and(Sr, Ca, Mg, Ba, Zn)(Al, B, In, Ga)(Si, Ge)N₃:Eu²⁺.

The ceramic phosphor plate may also have a general formula(Sr_(1−a−b)Ca_(b)Ba_(c)Mg_(d)Zn_(e))Si_(x)N_(y)O_(z):Eu_(a) ²⁺, wherein0.002≤a≤0.2, 0.0≤b≤0.25, 0.0≤c≤0.25, 0. 0≤d≤0.25, 0.0≤e≤0.25, 1.5≤x≤2.5,1.5≤y≤2.5 and 1.5≤z≤2.5. The ceramic phosphor plate may also have ageneral formula of MmAaBbOoNn:Zz where an element M is one or morebivalent elements, an element A is one or more trivalent elements, anelement B is one or more tetravalent elements, O is oxygen that isoptional and may not be in the phosphor plate, N is nitrogen, an elementZ that is an activator, n=2/3m+a+4/3b−2/3o, wherein m, a, b can all be 1and o can be 0 and n can be 3. M is one or more elements selected fromMg (magnesium), Ca (calcium), Sr (strontium), Ba (barium) and Zn (zinc),the element A is one or more elements selected from B (boron), Al(aluminum), In (indium) and Ga (gallium), the element B is Si (silicon)and/or Ge (germanium), and the element Z is one or more elementsselected from rare earth or transition metals. The element Z is at leastone or more elements selected from Eu (europium), Mg (manganese), Sm(samarium) and Ce (cerium). The element A can be Al (aluminum), theelement B can be Si (silicon), and the element Z can be Eu (europium).

The ceramic phosphor plate may also be an Eu²⁺ activated Sr—SiON havingthe formula (Sr_(1−a−b)Ca_(b)Ba_(c))Si_(x)N_(y)O_(x):Eu_(a), whereina=0.002-0.2, b=0.0-0.25, c=0.0-0.25, x=1.5-2.5, y=1.5-2.5.

The ceramic phosphor plate may also be a chemically-altered Ce: YAG(Yttrium Aluminum Garnet) phosphor that is produced by doping the Ce:YAG phosphor with the trivalent ion of praseodymium (Pr). The ceramicphosphor plate may include a main fluorescent material and asupplemental fluorescent material. The main fluorescent material may bea Ce: YAG phosphor and the supplementary fluorescent material may beeuropium (Eu) activated strontium sulfide (SrS) phosphor (“Eu:SrS”). Themain fluorescence material may also be a Ce: YAG phosphor or any othersuitable yellow-emitting phosphor, and the supplementary fluorescentmaterial may also be a mixed ternary crystalline material of calciumsulfide (CaS) and strontium sulfide (SrS) activated with europium((Ca_(x)Sr_(1_x))S:Eu²⁺). The main fluorescent material may also be aCe:YAG phosphor or any other suitable yellow-emitting phosphor, and thesupplementary fluorescent material may also be a nitrido-silicate dopedwith europium. The nitrido-silicate supplementary fluorescent materialmay have the chemical formula (Sr_(1−x−y−z)Ba_(x)Ca_(y))₂Si₅N₈:Eu_(z) ²⁺where 0≤x, y≤0.5 and 0≤z≤0.1.

The ceramic phosphor plate may also have a blend of any of the abovedescribed phosphors. More information can be found in U.S. Pat. Nos.7,462,502, 7,419,839, 7,544,309, 7,361,938, 7,061,024, 7,038,370,6,717,353, and 6,680,569, and U.S. Pat. App. Pub. No. 20060255710, whichare commonly assigned and incorporated by reference in their entirety.

Implementations of the disclosed subject matter may be applied to anyapplicable lighting device or system such as an automotive lightingcomponent including headlights, tail lights, and the like, flashlighting, LEDs, programmable lighting systems, and the like.

According to implementations of the disclosed subject matter, an ALDprocess may be used to coat a particle and may also be used to form acoating configured to bond multiple particles together. The followingdisclosure is associated with the ALD process along with hybridprocesses such as a sol-gel process followed by an ALD process, whichmay be incorporated by the implementations disclosed herein. Althoughthe following disclosure may generally be related to coating individualparticles, one of skilled in the art shall understand that some of theprocesses, as described in WO2016041838A1 and herein, can be utilizedwhen generating the three-dimensional films bonded via inorganiccoatings.

A method for providing luminescent particles with a hybrid coating isprovided, and includes: (i) providing a first coating layer (“firstcoating” or “sol-gel coating” or “sol-gel coating layer”) onto theluminescent particles by application of a sol-gel coating process,thereby providing coated luminescent particles; and (ii) providing asecond coating layer (“second coating” or “ALD coating” or “ALD coatinglayer”) onto the coated luminescent particles by application of anatomic layer deposition process, especially a method wherein the secondcoating layer comprises a multilayer with layers having differentchemical compositions, and wherein in the atomic layer depositionprocess a metal oxide precursor is, amongst others, selected from thegroup of metal oxide precursors of metals chosen from aluminum, hafnium,tantalum, zirconium, titanium, and silicon. The metal oxide precursorsmay include, trimethylaluminum, tetrakis (dimethylamino) hafnium,tetrakis (diethylamino) hafnium, tetrakis (methyl-ethyl amino) hafnium,tantalum chloride, pentakis (dimethylamino) tantalum, (t-butylamino)tris (methyl ethyl amino) tantalum, zirconium tetrachloride,tetrakis(dimethylamino) zirconium, tetramethoxy titanium, tetraethoxytitanium, silicon tetrachloride, (3-aminopropyl)triethoxysilane,tetraethoxy silane and oxygen source may be chosen from water and ozone(O₃). The layers in multilayers may comprise aluminum oxide, hafniumoxide, zirconium oxide, titanium oxide and silicon dioxide, preferablytantalum pentoxide and aluminum oxide. As shown in FIGS. 5a, 5b and 5c ,a luminescent core 102 comprises non-oxide, and an intermediate oxidelayer is present between the luminescent core 102 and the coating layer135. A sol-gel coating, involves providing agitating mixture of alcohol,ammonia, water, adding metal luminescent particles 100 and metalalkoxide precursor chosen from titanium alkoxide, silicon alkoxide, andaluminum alkoxide to the mixture and forming the coating (A) onluminescent particles 100 and retrieving from the mixture and heattreating the luminescent particles.

The precursor used in sol-gel coating may be silicon alkoxide precursorchosen from formula: R4-Si(—R1)(-R3)(-R2) (I). The silicon alkoxideprecursor is preferably chosen from trimethoxy silane, triethoxy silane,tetraethoxy silane, trimethoxy (methyl)silane and triethoxy(methyl)silane. R1-R3=hydrolyzable alkoxy moieties; and R4=1-6C linearalkyl moieties, hydrolyzable alkoxy moieties, and phenyl moiety.

According to implementations, luminescent/optically scattering particlesmay comprise a luminescent core, a first coating layer (“sol-gel coatinglayer”), especially having a first coating layer thickness (d1) in therange of 5-500 nm, especially 10-500 nm, yet even more especially 5-500nm, especially 10-500 nm, yet even more especially 20-500 nm, especially50-300 nm, such as at least 100 nm, and a second coating layer (“ALDcoating layer”) especially having a second coating layer thickness (d2)in the range of 5-250 nm, such as especially 5-200 nm, yet even moreespecially wherein the second coating layer comprises a multilayer withlayers having different, chemical compositions, and wherein themultilayer comprises one or more layers comprising an oxide of one ormore of Al, Hf, Ta, Zr, Ti and Si.

With such luminescent material, i.e. such luminescent materialcomprising these (hybrid coated) particles, a relative stableluminescent material is provided with quantum efficiencies close to oridentical to the virgin (non-coated) luminescent material and havingstabilities against water and/or (humid) air which are very high andsuperior to non-coated or non-hybrid coated luminescent particles.

The first coating layer may optionally include a multi-layer. However,the multi-layers of the first coating layer may be sol-gel layers.Therefore, the first layer is herein also indicated as sol-gel layer(thus optionally including a sol-gel multi-layer). The first coatinglayer especially comprises silicon oxide (especially SiO₂). An exampleof a multi-layer may include SiO₂—Al₂O₃ (sol-gel) multi-layer, such as astack of three or more (sol-gel) layers wherein SiO₂ and Al₂O₃alternate.

Likewise, the second coating layer may optionally include a multi-layer.However, the multi-layers of the second coating layer may all be ALDlayers. Therefore, the second layer is indicated as ALD layer (thusoptionally including an ALD multi-layer).

Especially, the second coating layer does comprise a multi-layer, seealso below. Further, especially the second coating layer is provided onthe first coating layer, without intermediate layers. Optionally, on thesecond coating layer, a further coating layer may be provided. Thesecond coating layer especially at least includes one or more aluminumoxide (especially Al₂O₃) coating layers. Especially, both the firstcoating layer and the second coating layer independently comprise metaloxides, though optionally also hydroxides may be included in the one ormore of these layers. Further, independently the first coating layer andthe second coating layer may include mixed oxide layers. Further, thecoating layers need not necessarily to be fully stoichiometric oxides,as is known in the art.

In general, the thickness of the first coating layer will be larger thanthe thickness of the second coating layer, such as at least 1.2, like atleast 1.5, like at least 2 times larger, or even at least 4 times or atleast 5 times larger. In a specific embodiment, the method of theinvention comprises (i) providing the first coating layer having a firstcoating layer thickness (d1) in the range of especially 20-500 nm, suchas at least 50 nm, even more especially 50-300 nm, such as at least 100nm, onto the luminescent particles by application of said sol-gelcoating process, thereby providing said coated luminescent particles;and (ii) providing the second coating layer having a second coatinglayer thickness (d2) in the range of especially 5-250 nm, such as 5-200nm, especially at least 10 nm, even more especially 10-100 nm, such as15-75 nm, yet more especially 15-50 nm, onto said coated luminescentparticles by application of said atomic layer deposition process. Hence,as indicated above, the luminescent particles comprise in an embodimenta luminescent core, a first coating layer having a first coating layerthickness (d1) in the range of especially 5-500 nm, especially 10-500nm, yet even more especially 20-500 nm, more especially 50-300 nm, suchas at least 100 nm, and a second coating layer having a second coatinglayer thickness (d2) in the range of especially 5-250 nm, even moreespecially 15-50 nm, such as in the range of 15-35 nm. It appears thatthicker first layers provide better results than thinner layers. Hence,especially the first coating layer has a first coating layer thicknessof at least 50 nm, such as at least about 100 nm.

The luminescent particles of interest may in principle include each typeof luminescent particles. However, especially of interest are those typeof luminescent particles that may be less stable in air or water or ahumid environment, such as e.g. (oxy)sulfides, (oxy)nitrides, etc.Hence, in an embodiment the luminescent particles comprise one or moreof a nitride luminescent material, an oxynitride luminescent material, ahalogenide luminescent material, an oxyhalogenide luminescent material,a sulfide luminescent material, and an oxysulfide luminescent material.Additionally or alternatively, the luminescent particles may comprise aselenide luminescent material. Hence, the term “luminescent particles”may also refer to a combination of particles of different types ofluminescent materials.

In a specific embodiment, the luminescent particles may be selected fromthe following group of luminescent material systems: MLiAl₃N₄:Eu (M=Sr,Ba, Ca, Mg), M₂SiO₄:Eu (M=Ba, Sr, Ca), MSe_(1−x)S_(x):Eu (M=Sr, Ca, Mg),MSr₂S₄:Eu (M=Sr, Ca), M₂SiF₆:Mn (M=Na, K, Rb), MSiAlN₃:Eu (M=Ca, Sr),M₈Mg(SiO₄)₄Cl₂:Eu (M=Ca, Sr), M₃MgSi₂O₈:Eu (M=Sr, Ba, Ca), MSi₂O₂N₂:Eu(M=Ba, Sr, Ca), M₂Si_(5−x)Al_(x)O_(x)N_(8−x):EU (M=Sr, Ca, Ba). However,other systems may also be of interested to protect by the hybridcoating. Also combinations of particles of two or more differentluminescent materials may be applied, such as e.g. a green or a yellowluminescent material in combination with a red luminescent material.

Terms like “M=Sr, Ba, Ca, Mg” indicates, as known in the art, that Mincludes one or more of Sr, Ba, Ca, and Mg. For instance, referring toMSiAlN₃:Eu (M=Ca, Sr), this may refer by way of examples to CaSiAlN₃:Eu,or to SrSiAlN₃:Eu, or to Ca_(0.8)Sr_(0.2)SiAlN₃:Eu, etc. etc. Further,the formula “MLiAl₃N₄:Eu (M=Sr, Ba, Ca, Mg),” is equal to the formula(Sr,Ba,Ca,Mg)LiAl₃N₄:Eu. Likewise this applies to the other hereinindicated formulas of inorganic luminescent materials.

In a further specific embodiment, the luminescent particles may beselected from the following group of luminescent material systems:M_(1−x−y−z)Z_(z)A_(a)B_(b)C_(c)D_(d)E_(e)N_(4−n)O_(n):ES_(x),RE_(y),with M=selected from the group consisting of Ca (calcium), Sr(strontium), and Ba (barium); Z selected from the group consisting ofmonovalent Na (sodium), K (potassium), and Rb (rubidium); A=selectedfrom the group consisting of divalent Mg (magnesium), Mn (manganese), Zn(zinc), and Cd (cadmium) (especially, A=selected from the groupconsisting of divalent Mg (magnesium), Mn (manganese), and Zn (zinc),even more especially selected from the group consisting of divalent Mg(magnesium), Mn (manganese); B=selected from the group consisting oftrivalent B (boron), Al (aluminum) and Ga (gallium); C=selected from thegroup consisting of tetravalent Si (silicon), Ge (germanium), Ti(titanium) and Hf (hafnium); D selected from the group consisting ofmonovalent Li (lithium), and Cu (copper); E selected for the groupconsisting of P (the element phosphor), V (vanadium), Nb (niobium), andTa (tantalum); ES=selected from the group consisting of divalent Eu(europium), Sm (samarium) and ytterbium, especially selected from thegroup consisting of divalent Eu and Sm; RE=selected from the groupconsisting of trivalent Ce (cerium), Pr (praseodymium), Nd (neodymium),Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy(dysprosium), Ho (holmium), Er (erbium), and Tm (thulium); with 0≤x≤0.2;0≤y≤0.2; 0<x+y≤0.4; 0≤z<1; 0≤n≤0.5; 0≤a≤4 (such as 2≤a≤3); 0≤b≤4; 0≤c≤4;0≤d≤4; 0≤e≤4; a+b+c+d+e=4; and 2a+3b+4c+d+5e=10−y−n+z. Especially,z≤0.9, such as z≤0.5. Further, especially x+y+z≤0.2.

The equations a+b+c+d+e=4; and 2a+3b+4c+d+5e=10−y−n+z, respectively,especially determine the Z, A, B, C, D and E cations and O and N anionsin the lattice and thereby define (also) the charge neutrality of thesystem. For instance, the charge compensation is covered by the formula2a+3b+4c+d+5e=10−y−n+z. It covers e.g. charge compensation by decreasingO content or charge compensation by substituting a C cation by a Bcation or a B cation by an A cation, etc. For example: x=0.01, y=0.02,n=0, a=3; then 6+3b+4c=10-0.02; with a+b+c=4: b=0.02, c=0.98.

As will be clear to a person skilled in the art, a, b, c, d, e, n, x, y,z are always equal to or larger than zero. When a is defined incombination with the equations a+b+c+d+e=4; and 2a+3b+4c+d+5e=10−y−n+z,then in principle, b, c, d, and e do not need to be defined anymore.However, for the sake of completeness, herein also 0≤b≤4; 0≤c≤4; 0≤d≤4;0≤e≤4 are defined.

Assume a system like SrMg₂Ga₂N₄:Eu. Here, a=2, b=2, c=d=e=y=z=n=0. Insuch system, 2+2+0+0+0=4 and 2*2+3*2+0+0+0=10−0−0+0=10. Hence, bothequations are complied with. Assume that 0.5 O is introduced. A systemwith 0.5 O can e.g. be obtained when 0.5 Ga—N is replaced by 0.5 Mg—O(which is a charge neutral replacement). This would result inSrMg_(2.5)Ga_(1.5)N_(3.5)O_(0.5):Eu. Here, in such system2.5+1.5+0+0+0=4 and 2*2.5+3*1.5+0+0+0=10−0−0.5+0=9.5. Hence, also hereboth equations are complied with.

As indicated above, in an advantageous embodiment d>0 and/or z>0,especially at least d>0. Especially, the phosphor comprises at leastlithium.

In yet another embodiment, 2≤a≤3, and especially also d=0, e=0 and z=0.In such instances, the phosphor is amongst others characterized bya+b+c=4; and 2a+3b+4c=10−y−n.

In a further specific embodiment, which may be combined with the formerembodiments e=0. In yet a further specific embodiment, which may becombined with the former embodiments, M is Ca and/or Sr.

Hence, in a specific embodiment, the phosphor has the formula M(Caand/or Sr)_(1−x−y)Mg_(a)Al_(b)Si_(c)N_(4−n)O_(n):ES_(x),RE_(y) (I), withES=selected from the group consisting of divalent Eu (europium) or Sm(samarium) or Yb (ytterbium); RE=selected from the group consisting oftrivalent Ce (cerium), Pr (praseodymium), Nd (neodymium), Sm (samarium),Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho(holmium), Er (erbium), and Tm (thulium), wherein y/x<0.1, especially<0.01, and n≤0.1, especially <0.01, even more especially <0.001, yeteven more especially <0.0001. Hence, in this embodiment, substantiallysamarium and or europium containing phosphors are described. Forinstance, when divalent Eu is present, with x=0.05, and for instance y1for Pr may be 0.001, and y2 for Tb may be 0.001, leading to any=y1+y2=0.002. In such instance, y/x=0.04. Even more especially, y=0.However, as indicated elsewhere when Eu and Ce are applied, the ratioy/x may be larger than 0.1.

The condition 0<x+y≤0.4 indicates that M may be substituted with intotal up to 40% of ES and/or RE. The condition “0<x+y≤0.4” incombination with x and y being between 0 and 0.2 indicates that at leastone of ES and RE are present. Not necessarily both types are present. Asindicated above, both ES and RE may each individually refer to one ormore subspecies, such as ES referring to one or more of Sm and Eu, andRE referring to one or more of Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,and Tm.

Especially, when europium is applied as divalent luminescent species ordopant (i.e. Eu²⁺), the molar ratio between samarium and europium(Sm/Eu) is <0.1, especially <0.01, especially <0.001. The same applieswhen europium in combination with ytterbium would be applied. Wheneuropium is applied as divalent luminescent species or dopant, the molarratio between ytterbium and europium (Yb/Eu) is <0.1, especially <0.01,especially <0.001. Would all three together be applied, then the samemolar ratios might apply, i.e. ((Sm+Yb)/Eu) is <0.1, especially <0.01,especially <0.001.

Especially, x is in the range of 0.001-0.2 (i.e. 0.001≤x≤0.2), like0.002-0.2, such as 0.005-0.1, especially 0.005-0.08. Especially in thecase of divalent Europium in the herein described systems, the molarpercentage may be in the range of 0.1-5% (0.001≤x≤0.05), such as 0.2-5%,like 0.5-2%. For other luminescent ions, x may (but is not necessarily)in embodiments be equal to or larger than 1% (x equal to or larger than0.01).

In a specific embodiment, the phosphor is selected from the groupconsisting of (Sr,Ca)Mg₃Si₄:Eu, (Sr,Ca)Mg₂Al₂N₄:Eu, (Sr,Ca)LiAl₃N₄:Euand (Sr,Ca)Li_(d)Mg_(a)Al_(b)N₄:Eu, with a, b, d as defined above.

As also indicated herein, the notation “(Sr,Ca)”, and similar notationswith other elements, indicates that the M-positions are occupied with Srand/or Ca cations (or other elements, respectively).

In a further specific embodiment the phosphor is selected from the groupconsisting of Ba_(0.95)Sr_(0.05)Mg₂Ga₂N₄:Eu, BaMg₂Ga₂N₄:Eu,SrMg₃SiN₄:Eu, SrMg₂Al₂N₄:Eu, SrMg₂Ga₂N₄:Eu, BaMg₃SiN₄:Eu, CaLiAl₃N₄:Eu,SrLiAl₃N₄:Eu, CaLi_(0.5)MgAl_(2.5)N₄:Eu, and SrLi_(0.5)MgAl_(2.5)N₄:Eu.Further (non-limiting) examples for such phosphors are e.g.(Sr_(0.8)Ca_(0.2))_(0.995)LiAl_(2.91)Mg_(0.09)N_(3.91)O_(0.09):Eu_(0.005);(Sr_(0.9)Ca_(0.1))_(0.905)Na_(0.09)LiAl₃N_(3.91)O_(0.09):Eu_(0.005);(Sr_(0.8)Ca_(0.03)Ba_(0.17))_(0.989)LiAl_(2.99)Mg_(0.01)N₄:Ce_(0.01),Eu_(0.001);Ca_(0.995)LiAl_(2.995)Mg_(0.005)N_(3.995)O_(0.005):Yb_(0.005) (YB(II));Na_(0.995)MgAl₃N₄:Eu_(0.01);Na_(0.895)Ca_(0.1)Mg_(0.9)Li_(0.1)Al₃N₄:Eu_(0.005);Sr_(0.99)LiMgAlSiN₄:Eu_(0.01);Ca_(0.995)LiAl_(2.955)Mg_(0.045)N_(3.96)O_(0.04):Ce_(0.005);(Sr_(0.9)Ca_(0.1))_(0.998)Al_(1.99)Mg_(2.01)N_(3.99)O_(0.01):Eu_(0.002);(Sr_(0.9)Ba_(0.1))_(0.998)Al_(1.99)Mg_(2.01)N_(3.99)O_(0.01):Eu_(0.002).

In a further specific embodiment, the phosphor is selected from thegroup consisting of (Sr,Ca)Mg₃SiN₄:Eu and (Sr,Ca)Mg₂Al₂N₄:Eu. In yetanother specific embodiment, the phosphor is selected from the groupconsisting of Ba_(0.95)Sr_(0.05)Mg₂Ga₂N₄:Eu, BaMg₂Ga₂N₄:Eu,SrMg₃SiN₄:Eu, SrMg₂Al₂N₄:Eu, SrMg₂Ga₂N₄:Eu, and BaMg₃SiN₄:Eu.Especially, these phosphors, and even more especially (Sr,Ca)Mg₃SiN₄:Euand (Sr,Ca)Mg₂Al₂N₄:Eu may be phosphors having good luminescentproperties, amongst others in terms of spectral position anddistribution of the luminescence.

Of especial interest are phosphors wherein the phosphor complies with0≤x≤0.2, y/x<0.1, M comprises at least Sr, z≤0.1, a≤0.4, 2.5≤b≤3.5, Bcomprises at least Al, c≤0.4, 0.5≤d≤1.5, D comprises at least Li, e≤0.4,n≤0.1, and wherein ES at least comprises Eu. Especially, y+z≤0.1.Further, especially x+y+z≤0.2. Further, especially a is close to 0 orzero. Further, especially b is about 3. Further, especially c is closeto 0 or zero. Further, especially d is about 1. Further, especially e isclose to 0 or zero. Further, especially n is close to 0 or zero.Further, especially y is close to 0 or zero. Especially good systems, interms of quantum efficiency and hydrolysis stability are those withz+d>0, i.e. one or more of Na, K, Rb, Li and Cu(I) are available,especially at least Li, such as e.g. (Sr,Ca)LiAl₃N₄:Eu and(Sr,Ca)Li_(d)Mg_(a)Al_(b)N₄:Eu, with a, b, d as defined above. In afurther specific embodiment the phosphor is selected from the groupconsisting of CaLiAl₃N₄:Eu, SrLiAl₃N₄:Eu, CaLi_(0.5)MgAl_(2.5)N₄:Eu, andSrLi_(0.5)MgAl_(2.5)N₄:Eu. Further phosphors of special interest are(Sr,Ca,Ba)(Li,Cu)(Al,B,Ga)₃N₄:Eu, which comprises as M ion at least Sr,as B ion at least Al, and as D ion at least Li.

Hence, in a specific embodiment, the luminescent particles comprise aluminescent material selected from the SrLiAl₃N₄:Eu²⁺ class. The term“class” herein especially refers to a group of materials that have thesame crystallographic structure(s). Further, the term “class” may alsoinclude partial substitutions of cations and/or anions. For instance, insome of the above-mentioned classes Al—O may partially be replaced bySi—N (or the other way around). Examples of the SrLiAl₃N₄:Eu²⁺ class areprovided above. However, other luminescent materials may thus also bepossible.

Such luminescent particles may have a number averaged particle sizeselected from the range of 0.1-50 μm, such as in the range of 0.5-40 μm,such as especially in the range of 0.5-20 μm. Hence, the luminescentcore may have dimensions such as at maximum about 500 μm, such as atmaximum 100 μm, like at maximum about 50 μm. especially with the largerparticles sizes, substantially only individual particles may be coated,leading thus to luminescent core dimensions in the order of 50 μm orsmaller. Hence, the invention is direct to the coating of particles. Thedimensions of the luminescent core may substantially be smaller whennanoparticles or quantum dots are used as basis for the particulateluminescent material. In such instance, the cores may be smaller thanabout 1 μm or substantially smaller (see also below for the dimensionsof the QDs). Alternatively or additionally, the luminescent particlesinclude luminescent quantum dots. The term “quantum dot” or “luminescentquantum dot” may in embodiments also refer to a combination of differenttype of quantum dots, i.e. quantum dots that have different spectralproperties. The QDs are herein also indicated as “wavelength converternanoparticles” or “luminescent nanoparticles”. The term “quantum dots”especially refer to quantum dots that luminesce in one or more of theUV, visible and IR (upon excitation with suitable radiation, such as UVradiation). The quantum dots or luminescent nanoparticles, which areherein indicated as wavelength converter nanoparticles, may for instancecomprise group II-VI compound semiconductor quantum dots selected fromthe group consisting of (core-shell quantum dots, with the core selectedfrom the group consisting of) CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS,HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe,HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe,HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS,HgZnSeTe and HgZnSTe. In another embodiment, the luminescentnanoparticles may for instance be group III-V compound semiconductorquantum dots selected from the group consisting of (core-shell quantumdots, with the core selected from the group consisting of) GaN, GaP,GaAs, AlN, AlP, AlAs, InN, InP, InGaP, InAs, GaNP, GaNAs, GaPAs, ANP,AlNAs, AlPAs, InNP, InNAs, InPAs, GaAlNP, GaAlNAs, GaAlPAs, GaInNP,GaInNAs, GaInPAs, InAlNP, InAlNAs, and InAlPAs. In yet a furtherembodiment, the luminescent nanoparticles may for instance be I-III-VI2chalcopyrite-type semiconductor quantum dots selected from the groupconsisting of (core-shell quantum dots, with the core selected from thegroup consisting of) CuInS₂, CuInSe₂, CuGaS₂, CuGaSe₂, AgInS₂, AgInSe₂,AgGaS₂, and AgGaSe₂. In yet a further embodiment, the luminescentnanoparticles may for instance be (core-shell quantum dots, with thecore selected from the group consisting of) I-V-VI2 semiconductorquantum dots, such as selected from the group consisting of (core-shellquantum dots, with the core selected from the group consisting of)LiAsSe₂, NaAsSe₂ and KAsSe₂. In yet a further embodiment, theluminescent nanoparticles may for instance be core-shell quantum dots,with the core selected from the group consisting of) group (IV-VIcompound semiconductor nano crystals such as SbTe. In a specificembodiment, the luminescent nanoparticles are selected from the groupconsisting of (core-shell quantum dots, with the core selected from thegroup consisting of) InP, CuInS₂, CuInSe₂, CdTe, CdSe, CdSeTe, AgInS₂and AgInSe₂. In yet a further embodiment, the luminescent nanoparticlesmay for instance be one of the group (of core-shell quantum dots, withthe core selected from the group consisting of) II-VI, III-V, I-III-Vand IV-VI compound semiconductor nano crystals selected from thematerials described above with inside dopants such as ZnSe:Mn, ZnS:Mn.The dopant elements could be selected from Mn, Ag, Zn, Eu, S, P, Cu, Ce,Tb, Au, Pb, Tb, Sb, Sn and Tl. Herein, the luminescent nanoparticlesbased luminescent material may also comprise different types of QDs,such as CdSe and ZnSe:Mn.

It appears to be especially advantageous to use II-VI quantum dots.Hence, in an embodiment the semiconductor based luminescent quantum dotscomprise II-VI quantum dots, especially selected from the groupconsisting of (core-shell quantum dots, with the core selected from thegroup consisting of) CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe,CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS,CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS,CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe andHgZnSTe, even more especially selected from the group consisting of CdS,CdSe, CdSe/CdS and CdSe/CdS/ZnS.

In an embodiments, the wavelength converter nanoparticles have anaverage particle size in a range from about 1 to about 1000 nanometers(nm), and preferably in a range from about 1 to about 100 nm. In anembodiment, nanoparticles have an average particle size in a range fromabout 1 to about 20 nm. In an embodiment, nanoparticles have an averageparticle size in a range from about 1 to about 10 nm. The luminescentnanoparticles (without coating) may have dimensions in the range ofabout 2-50 nm, such as 2-20 nm, especially 2-10 nm, even more especially2-5 nm; especially at least 90% of the nanoparticles have dimension inthe indicated ranges, respectively, (i.e., e.g. at least 90% of thenanoparticles have dimensions in the range of 2-50 nm, or especially atleast 90% of the nanoparticles have dimensions in the range of 2-5 nm).The term “dimensions” especially relate to one or more of length, width,and diameter, dependent upon the shape of the nanoparticle. Typical dotsare made of binary alloys such as cadmium selenide, cadmium sulfide,indium arsenide, and indium phosphide. However, dots may also be madefrom ternary alloys such as cadmium selenide sulfide. These quantum dotscan contain as few as 100 to 100,000 atoms within the quantum dotvolume, with a diameter of 10 to 50 atoms. This corresponds to about 2to 10 nanometers. For instance, spherical particles such as CdSe, InP,or CuInSe₂, with a diameter of about 3 nm may be provided. Theluminescent nanoparticles (without coating) may have the shape ofspherical, cube, rods, wires, disk, multi-pods, etc., with the size inone dimension of less than 10 nm. For instance, nanorods of CdSe withthe length of 20 nm and a diameter of 4 nm may be provided. Hence, in anembodiment the semiconductor based luminescent quantum dots comprisecore-shell quantum dots. In yet another embodiment, the semiconductorbased luminescent quantum dots comprise dots-in-rods nanoparticles. Acombination of different types of particles may also be applied. Here,the term “different types” may relate to different geometries as well asto different types of semiconductor luminescent material. Hence, acombination of two or more of (the above indicated) quantum dots orluminescent nano-particles may also be applied.

In an embodiment, nanoparticles can comprise semiconductor nanocrystalsincluding a core comprising a first semiconductor material and a shellcomprising a second semiconductor material, wherein the shell isdisposed over at least a portion of a surface of the core. Asemiconductor nanocrystal including a core and shell is also referred toas a “core/shell” semiconductor nanocrystal. Any of the materialsindicated above may especially be used as core. Therefore, the phrase“core-shell quantum dots, with the core selected from the groupconsisting of” is applied in some of the above lists of quantum dotmaterials. The term “core-shell” may also refer to “core-shell-shell”,etc., including gradient alloy shell, or dots in rods, etc.

For example, the semiconductor nanocrystal can include a core having theformula MX, where M can be cadmium, zinc, magnesium, mercury, aluminum,gallium, indium, thallium, or mixtures thereof, and X can be oxygen,sulfur, selenium, tellurium, nitrogen, phosphorus, arsenic, antimony, ormixtures thereof. Examples of materials suitable for use assemiconductor nanocrystal cores include, but are not limited to, ZnO,ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgS, MgSe, GaAs, GaN, GaP, GaSe,GaSb, HgO, HgS, HgSe, HgTe, InAs, InN, InP, InGaP, InSb, AlAs, AlN, AlP,AlSb, TlN, TlP, TlAs, TlSb, PbO, PbS, PbSe, PbTe, Ge, Si, an alloyincluding any of the foregoing, and/or a mixture including any of theforegoing, including ternary and quaternary mixtures or alloys.

The shell can be a semiconductor material having a composition that isthe same as or different from the composition of the core. The shellcomprises an overcoat of a semiconductor material on a surface of thecore semiconductor nanocrystal can include a Group IV element, a GroupII-VI compound, a Group II-V compound, a Group III-VI compound, a GroupIII-V compound, a Group IV-VI compound, a Group I-III-VI compound, aGroup II-IV-VI compound, a Group II-IV-V compound, alloys including anyof the foregoing, and/or mixtures including any of the foregoing,including ternary and quaternary mixtures or alloys. Examples include,but are not limited to, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgS,MgSe, GaAs, GaN, GaP, GaSe, GaSb, HgO, HgS, HgSe, HgTe, InAs, InN, InP,InGaP, InSb, AlAs, AlN, AlP, AlSb, TlN, TlP, TlAs, TlSb, PbO, PbS, PbSe,PbTe, Ge, Si, an alloy including any of the foregoing, and/or a mixtureincluding any of the foregoing. For example, ZnS, ZnSe or CdSovercoatings can be grown on CdSe or CdTe semiconductor nanocrystals. Anovercoating process is described, for example, in U.S. Pat. No.6,322,901. By adjusting the temperature of the reaction mixture duringovercoating and monitoring the absorption spectrum of the core, overcoated materials having high emission quantum efficiencies and narrowsize distributions can be obtained. The overcoating may comprise one ormore layers. The overcoating comprises at least one semiconductormaterial which is the same as or different from the composition of thecore. Preferably, the overcoating has a thickness from about one toabout ten monolayers. An overcoating can also have a thickness greaterthan ten monolayers. In an embodiment, more than one overcoating can beincluded on a core.

In an embodiment, the surrounding “shell” material can have a band gapgreater than the band gap of the core material. In certain otherembodiments, the surrounding shell material can have a band gap lessthan the band gap of the core material. In an embodiment, the shell canbe chosen so as to have an atomic spacing close to that of the “core”substrate. In certain other embodiments, the shell and core materialscan have the same crystal structure.

Examples of semiconductor nanocrystal (core)shell materials include,without limitation: red (e.g., (CdSe)ZnS (core)shell), green (e.g.,(CdZnSe)CdZnS (core)shell, etc.), and blue (e.g., (CdS)CdZnS (core)shell(see further also above for examples of specific wavelength converternanoparticles, based on semiconductors).

Therefore, in an embodiment the luminescent particles comprises aluminescent material selected from the group consisting of luminescentquantum dots comprising one or more core materials selected from thegroup consisting of CdS, CdSe, ZnS, and ZnSe. Hence, in an embodimentthe luminescent particles may also be selected from the group ofluminescent nanoparticles such as quantum dots or quantum rods ofcomposition MX (M=Cd, Zn, X=Se, S). Such particles may have a numberaveraged particle size (i.e., especially length/width/height, diameter),selected from the range of 1-50 nm.

As indicated above, the first coating layer that typically has anaverage thickness in the 5-500 nm, especially 10-500 nm, yet even moreespecially 20-500 nm, even more especially 50-300 nm range, is formed bya sol-gel type process. In such process, an inorganic network is formedfrom a homogeneous solution of precursors by subsequent hydrolysis toform a sol (colloidal suspension) and condensation to then form a gel(cross-linked solid network) that is chemically bonded to the powdersurfaces. Preferably, the first coating material is silica and thesol-gel deposition method corresponds to the so-called Stöber reactionas described in Stöber, W., A. Fink, et al. “Controlled growth ofmonodisperse silica spheres in the micron size range.” Journal ofColloid and Interface Science 26(1): 62-69. To this end the luminescentmaterial is dispersed in an alcohol such as an aliphatic alcohol R—OHsuch as methanol CH₃OH, ethanol C₂H₅OH or iso-propanol C₃H₇OH followedby addition of ammonia (NH₃ solution in water) and a silicon alkoxideprecursor. The silicon alkoxide precursor dissolves in thealcohol+ammonia mixture and starts to hydrolyze. A conformal silicacoating is formed on top of the particle surfaces by reaction of thehydrolyzed, yet dissolved sol species with reactive groups of theparticle surfaces (e.g. amine or silanol groups) followed by a seededgrowth process that consists of hydrolysis, nucleation and condensationreactions steps.

The silicon alkoxide precursor is selected from a group of compoundsthat is formed by

wherein a) R1, R2, R3 are hydrolysable alkoxy groups and R4 is selectedfrom the group of C1-C6 linear alkyl groups, hydrolysable alkoxy groupsand a phenyl group, or b) R1, R2, R3 are individually selected from—OCH₃ and —OC₂H₅ and R4 is selected from —CH₃, —C₂H₅, —OCH₃, —OC₂H₅ anda phenyl group. Optionally, the silicone based polymer is obtained froma material from the group of:

Hence, the silicon alkoxide precursor is selected from a group may beselected from this group. Especially, the silicon alkoxide precursor isselected from the group of Si(OCH₃)₄ or Si(OC₂H₅)₄, more especiallySi(OC₂H₅)₄ is used as silicone alkoxide precursor. Similar precursors,but based on another metal such as e.g. Al may also be used.

A typical first coating process may comprise the following stages: (a)the luminescent powder is suspended in an alcohol—aqueous ammoniasolution mixture while stirring or sonication. To improve particledispersion, the powder can also first be mixed with alcohol and a smallamount of a silicon (or other metal) alkoxide before the ammoniasolution is added. (b) A silicon (or other metal) alkoxide precursor isadded under agitation of the suspension. Typical concentrations ofsilicone (or other metal) alkoxide, ammonia and water in the alcoholsolvent are 0.02-0.7, 0.3-1.5, and 1-16 mole/l, respectively. (c) Thesuspension is stirred or sonicated until the coating has formed. (d) Thecoated powder is washed with alcohol and dried followed by calcinationin air or vacuum at 200-300° C.

Hence, in an embodiment the sol-gel coating process comprises: (ia)providing a mixture of an alcohol, ammonia, water, the luminescentparticles and a metal alkoxide precursor while agitating the mixture,and allowing the first coating to be formed on the luminescentparticles, wherein the metal alkoxide precursor is especially selectedfrom the group consisting of an titanium alkoxide, a silicon alkoxide,and an aluminum alkoxide; and (ib) retrieving the luminescent particlesfrom the mixture and optionally subjecting the luminescent particles toa heat treatment to provide said coated luminescent particles. Theprocess of retrieving the (coated) luminescent materials from themixture may e.g. include one or more of filtration, centrifuging,decanting (the liquid over a precipitate), etc. The heat treatment mayinclude one or more of drying and calcination, especially both, i.e.e.g. a drying stage at a temperature in the range of 70-130° C. followedby a calcination stage (in air; or vacuum or an (other) inertatmosphere). Hence, during part of the time of the heat treatment, the(coated) luminescent may be in an inert environment, such as vacuum, orone or more of N₂ and a noble gas, etc. The heat treatment seems toimprove the stability of the luminescent material. Further, as indicatedabove in the sol-gel coating process a silicon (or other metal; thoughthe formula below refers to Si) alkoxide especially a precursor may beused selected from the group of compounds consisting of:

wherein R1, R2, R3 are selected from the group consisting ofhydrolysable alkoxy moieties and R4 is selected from the groupconsisting of C1-C6 linear alkyl moieties, hydrolysable alkoxy moieties,and a phenyl moiety. Optionally other ligands than alkoxides may beapplied in precursor for the sol-gel process.

The particles obtained with sol-gel coating process may optionallyinclude more than one nucleus. For instance in the case of quantum dots,agglomerates with a sol-gel coating or first coating layer may beobtained. Hence, the silica precursor (or other metal oxide precursor)can also coat multiple QDs with thin single shells to form a coatedagglomerate. This may amongst others depend upon the concentration ofthe quantum dots, etc.

Above, the precursors for the sol-gel coating are especially describedin relation to a silicon alkoxide precursor. However, also aluminum (oranother metal) alkoxide precursor(s) may be applied. Further, also acombination of two or more chemically different precursors may beapplied for providing the sol-gel coating layer or first coating layer.

The term “first coating process” may also relate to a plurality of firstcoating processes. With a plurality of first coating processes one mayprovide a (multi-)layer substantially comprising the same compositionthrough the entire layer thickness (when e.g. in the first coatingprocess each coating stage or step includes depositing substantially thesame material), or may provide a multi-layer with two or more layershaving different compositions, such as a stack of two or more (sol-gel)layers with two or more different compositions, respectively. An examplemay e.g. be a SiO₂—A₂O₃ (sol-gel) multi-layer, such as a stack of threeor more (sol-gel) layers wherein SiO₂ and Al₂O₃ alternate (see alsoabove).

As indicated above, the second coating layer may typically have a layerthickness in the 5-250 nm, especially 15-75 nm range. The layer may beformed by an atomic layer deposition type process. In such process apolymeric network is formed by reaction of a metal oxide precursor withan oxygen source such as water and/or ozone in the gas phase. Unlike inthe sol-gel process the ALD reaction is split in (at least) two parts.In a first step the metal (oxide) precursor is fed into a(n ALD) reactorand adsorbs and/or reacts with reactive groups on the particle surfacesand substantially all non-reacted or adsorbed precursor molecules areremoved by reactor purging. In a second step the oxygen source is fedinto the reactor and reacts with the metal source on the particlesurfaces followed by purging of the reactor to remove substantially allremaining oxygen source molecules and hydrolysis products formed bycondensation reactions. The two steps lead to formation of an atomiclayer (or monolayer) because of the self-limiting nature of the surfacereaction. These atomic layer reaction steps are repeated multiple timesto form the final ALD coating. The term metal oxide precursor especiallyindicates a precursor of the metal oxide. The precursor itself may notbe a metal oxide, but may e.g. include metal organic molecule. Hence,especially the metal (oxide) precursors for ALD may typically includemetal halides, alkoxides, amides, and other metal (organic) compounds.

The step by step nature of the ALD process allows to easily depositdefined layer thicknesses. The ALD process further allows it to depositlayers of different composition by consecutively feeding different metaloxide precursor into the reactor to form multicomponent layers ornanolaminates. Hence, in a specific embodiment the second layercomprises a multilayer (see also below).

For the ALD process, amongst others a fluidized bed reactor may beapplied. Hence, in a specific embodiment the second coating layer isprovided by application of said atomic layer deposition process. In anembodiment, a static powder bed is used for ALD coating of the sol-gelcoated luminescent powder particles. However, also a fluidized bed maybe applied. Other type of reactors may also be applied. Particleagglomeration may substantially be prevented by applying a first sol-gelcoating with a structured, nanoporous surface. The process can easilyscaled up and nearly no powder loss during ALD coating is observed.Commercially available ALD reactors for powder coating are e.g. sold byPicosun Oy with e.g. a cartridge sample holder (POCA™). A system thatmay be used for ALD is e.g. described in WO 2013171360 Al, though othersystems may also be applied.

A (non-limited) number of suitable materials for the ALD second coatinglayer are listed in the following table:

Oxide Oxygen Deposition material Metal (oxide_ precursor source T [° C.]Al₂O₃ Al(CH₃)₃ (TMA) H₂O or O₃ 100-400 or HAl(CH₃)₂ HfO₂ Hf(N(CH₃)₂)₄ orH₂O  80-300 Hf(N(CH₂CH₃)₂)₄ Ta₂O₅ TaCl₅ or Ta(N(CH₃)₂)₅ H₂O  80-300 ZrO₂ZrCl₄ or Zr(N(CH₃)₂)₄ H₂O  80-300 TiO₂ TiCl₄, Ti(OCH₃)₄ or H₂O  80-300Ti(OEt)₄ SiO₂ SiCl₄, H₂N(CH₂)₃Si(OEt)₃ H₂O or O₃ 150-300 or Si(OEt)₄

Alternatively or additionally, niobium oxide (especially Nb₂O₅) oryttrium oxide (Y₂O₃) may be applied. Metal precursors thereof are e.g.,tert-butylimido)-tris (diethylamino)-niobium, NbF₅, or NbCl₅, andTris(ethylcyclopentadienyl) Yttrium, respectively.

However, other materials may also be applied. Hence, in the atomic layerdeposition process a metal oxide precursor may especially be selectedfrom the group of metal oxide precursors of metals selected from thegroup consisting of Al, Hf, Ta, Zr, Ti and Si. Alternatively oradditionally, one or more of Ga, Ge, V and Nb may be applied. Even moreespecially, alternating layers of two or more of these precursors areapplied, wherein at least one precursor is selected from the groupconsisting of an Al metal oxide precursor and an Si metal oxideprecursor, especially an Al metal oxide metal oxide precursor, andanother precursor is selected from the group consisting of a Hf metaloxide precursor, a Ta metal oxide precursor, a Zr metal oxide precursorand a Ti metal oxide precursor, especially selected from the groupconsisting of a Hf metal oxide precursor, a Ta metal oxide precursor,and a Zr metal oxide precursor, even more especially a Ta metal oxideprecursor. Especially Hf, Zr, and Ta appear to provide relatively lighttransmissive layers, whereas Ti, for instance, may provide relativelyless light transmissive layers. Processing with Ta, Hf and Zr seems tobe relatively easier than Si, for instance. The terms “oxide precursor”or “metal oxide precursor” or “metal (oxide) precursor” may also referto a combination of two or more chemically different precursors. Theseprecursors especially form an oxide upon reaction with the oxygen source(and are therefore indicated as metal oxide precursor).

For instance, silanol groups (assuming a silica first coating layer) atthe nanoporous surface of the sol-gel first coating layer act asreactive sites during ALD of the initial layers. In an embodiment,alumina is deposited by using Al(CH₃)₃ (TMA) as metal oxide precursorand (subsequently exposure to) water as the oxygen source. In the firstreaction step, TMA reacts with surface silanol groups of the silica solgel layer according to:

≡SiOH+Al(CH₃)₃→≡Si—O—Al(CH₃)₂+CH₄

Water then reacts in the second reaction step with the metal oxideprecursor by hydrolysis followed by condensation reactions:

≡Si—O—Al(CH₃)₂+2H₂O→≡Si—O—Al(OH)₂+2CH₄

2≡Si—O—Al(OH)₂→≡Si—O—Al(OH)—O—Al(OH)—O—Si≡+H₂O

It turned out that deposition temperatures in the 200-350° C. range aremost suitable for alumina ALD on the first coating layer, preferably thetemperature is in the 250-300° C. range. Similar temperatures may beapplied for ALD of other metal oxide precursors for the ALD layer(s).

Especially, the ALD alumina (or other metal oxide) layer has a thicknessof 5-120 nm, more especially a thickness of 10-75 nm, yet even moreespecially a thickness in the 15-50 nm range.

Water gas penetration barrier properties of alumina ALD layers can befurther improved by depositing at least one additional layer of adifferent oxide material such as ZrO₂, TiO₂, Y₂O₃, Nb₂O₅, HfO₂, Ta₂O₅.Especially, the thickness of the additional material layer is in therange 1-40 nm, more preferably in the range 1-10 nm. Even more preferredare nanolaminate stacks of alternating layers of Al₂O₃ and a secondoxide material from the group of ZrO₂, TiO₂, Y₂O₃, Nb₂O₅, HfO₂, Ta₂O₅. Asuitable nanolaminate stack may be e.g. 20×(1 nm Al₂O₃ (10 ALD cycles)+1nm ZrO₂ (11 ALD cycles)) deposited at 250° C. to form a 40 nm thicknanolaminated 2^(nd) coating on top of the first sol-gel coating.

The invention especially provides in an embodiment a method wherein thesecond coating layer comprises a multilayer with layers having differentchemical compositions, and wherein in the atomic layer depositionprocess a metal oxide precursor is—amongst others—selected from thegroup of metal oxide precursors of metals selected from the groupconsisting of Al, Hf, Ta, Zr, Ti, Si, Ga, Ge, V and Nb, especially themetal oxide precursor is selected from the group of metal oxideprecursors of metals selected from the group consisting of Al, Hf, Ta,Zr, Ti and Si. Also combinations of two or more of such precursors maybe used, e.g. a multilayer comprising alumina—a mixoxide of zirconiumand hafnium—alumina, etc.

Hence, in an embodiment the second coating layer may comprise amultilayer with layers having different chemical compositions, andwherein the multilayer comprises one or more layers comprising an oxideof one or more of Al, Hf, Ta, Zr, Ti, Si, Ga, Ge, V, and Nb, especiallywherein the multilayer comprises one or more layers comprising an oxideof one or more of Al, Hf, Ta, Zr, Ti and Si. One or more layers of suchmulti-layers may also include mixoxides, such as indicated above.

Especially the method is applied such that a(n ALD) multi-layer coatingis obtained including at least two (ALD) layers (“AB”), even moreespecially at least three layers (e.g. “ABA”), yet even more at leastfour layers. Yet more especially, at least a stack comprising two ormore stack of subsets of two (ALD) layers (“AB”) is applied, such as(AB)_(n), wherein n is 2 or more, such as 2-20, like 2-10.

Especially, at least one of the layers of the multi-layer comprises oneor more of an oxide of Al and Si (including a combination thereof), andat least one of the layers of the multi-layer comprises one or more ofan oxide of Hf, Ta, Zr, Ti, Ga, Ge, V, and Nb. Such layer may optionallyalso include Al, Hf, Ta, Zr, Ti, Si, Ga, Ge, V, and Nb, wherein Si or Alare in a layer together with one or more of the other indicatedelements, when the other layer(s) of the multi-layer comprise an oxideof silica or alumina, respectively. The term “ALD multi-layer” or“multi-layer” as indicated above especially refers to layers havingdifferent chemical compositions. The phrase “layers having differentchemical compositions” indicates that there are at least two layershaving different chemical compositions, such as in the case of “ABC”, orin the case of (AB)_(n).

Specific examples of (AB)_(n) include multi-layers wherein A is selectedfrom one or more of an oxide of Si and Al, especially Al, and wherein Bis selected from one or more of an oxide of Al, Hf, Ta, Zr, Ti, Si, Ga,Ge, V, and Nb, wherein Si or Al are in a layer together with one or moreof the other indicated elements, when the other layer(s) of themulti-layer comprise an oxide of silica or alumina, respectively,especially wherein B is selected from one or more of an oxide of Hf, Ta,Zr, Ti, Ga, Ge, V, and Nb, yet even more especially wherein B isselected from one or more of an oxide of Hf, Ta, Zr, and Ti, moreespecially wherein B is selected from one or more of an oxide of Hf, Ta,and Zr.

This ALD multi-layer is thus especially provided on the sol-gel layer.Further, as indicated above, on top of the ALD multi-layer, optionallyone or more further layers may be applied.

Hence, in a specific embodiment the second coating layer comprises amulti-layer with a stack of layers, with adjacent layers havingdifferent chemical compositions.

Especially, the layers of the multi layer have each independentlythicknesses in the range of 1-40 nm, especially 1-10 nm. Further,especially, the multi-layer comprises one or more alumina layers and oneor more metal oxide layers, with the metal selected from the group ofHf, Ta, Zr and Ti.

Therefore, in a specific embodiment in the atomic layer depositionprocess a metal oxide precursor selected from the group consisting ofAl(CH₃)₃, HAl(CH₃)₂, Hf(N(CH₃)₂)₄, Hf(N(CH₂CH₃)₂)₄, Hf[N(CH₃)(CH₂CH₃)]₄,TaCl₅, Ta(N(CH₃)₂)₅, Ta{[N(CH₃)(CH₂CH₃)]₃N(C(CH₃)₃)}, ZrCl₄,Zr(N(CH₃)₂)₄, TiCl₄, Ti(OCH₃)₄, Ti(OCH₂CH₃)₄, SiCl₄,H₂N(CH₂)₃Si(OCH₂CH₃)₃, and Si(OCH₂CH₃)₄, and an oxygen source selectedfrom the group consisting of H₂O and O₃ are applied. As indicated above,also two or more different metal oxide precursors and/or two or moredifferent oxygen sources may be applied.

Further, in yet an embodiment of the method in the atomic layerdeposition process a multi-layer is provided, with layers havingdifferent chemical compositions, wherein one or more layers comprisetantalum oxide (especially Ta₂O₅). Hence, the invention also provides inan embodiment luminescent material, wherein the second coating layercomprises a multilayer with layers having different chemicalcompositions, wherein one or more layers may especially comprise Ta₂O₅.Further, in an embodiment of the method in the atomic layer depositionprocess a multi-layer is provided, with layers having different chemicalcompositions, wherein one or more layers comprise one or more oftantalum oxide (especially Ta₂O₅), hafnium oxide and zirconium oxide.Hence, the invention also provides in an embodiment luminescentmaterial, wherein the second coating layer comprises a multilayer withlayers having different chemical compositions, wherein one or morelayers may especially comprise one or more of tantalum oxide, hafniumoxide and zirconium oxide. For instance, the multilayer stack may alsoinclude an stack with alternating layers wherein e.g. alumina alternateswith one or more of tantalum oxide (especially Ta₂O₅), hafnium oxide andzirconium oxide, such as a stack comprising e.g. alumina-tantalumoxide-alumina-Hafnia-alumina-tantalum oxide etc.

Further, it appeared that when first an ALD coating was provided on theluminescent material particles (thus when e.g., preceding a subsequentthe sol-gel layer) the ALD layer was less uniform than desirable. Hence,to obtain a good ALD layer, the ALD layer thickness may have to beincreased more than in principle would be necessary, which may lead toan unnecessary reduction in transmission (even though in some casessmall). Further, it appeared that an ALD coating coats more easily to asol-gel obtained coating, whereas a sol-gel coating may less easily coatto an ALD coating. Further, a sol-gel process on an ALD layer might beharmful for the ALD layer.

The use of a final layer, i.e. a layer further away of the luminescentcore comprising a metal oxide layer, with the metal selected from thegroup of Hf, Ta, Zr and Ti, seems especially beneficial in terms ofstability. Further, using thin individual layers, such as thinner thanabout 10 nm, such as at least 5 nm, like at least 1 nm, also seems toadd to the stability of the luminescent material.

Hence, the total layer thickness of the second coating layer isespecially in the range of 5-250 nm, such as 10-200 nm, especially like15-120 nm, such as 15-50 nm, like 20-75 nm.

When a non-oxide luminescent material is applied, during and/or beforethe method of the invention, i.e. especially the first coating process,an oxygen containing layer may be formed on the particles of theluminescent materials, leading to an intermediate oxygen containinglayer between the core and the first coating layer. Hence, in a furtherembodiment the luminescent core comprises a non-oxide, and there is anintermediate oxide layer between the luminescent core and the firstcoating layer. The thickness of this intermediate layer may be in therange of 0.5-50 nm, such as 1-20 nm.

The layer thicknesses described herein are especially average layerthicknesses. However, especially at least 50%, even more especially atleast 80%, of the area of the respective layers have such indicatedlayer thickness. Especially this indicates that under at least 50% ofthe area of such layer, such thickness will be found.

The first coating layer and the second coating layer are lighttransmitting which means that at least a portion of the light, whichimpinges on the respective layers, is transmitted through the respectivelayer. Thus, the first layer and the second layer may be fully orpartially transparent, or may be translucent. More than 90% of the(visible) light which impinges on the coating layers may be transmittedthrough the coating layers. The first coating layer and/or the secondcoating layer may be light transmitting because of characteristics ofthe materials of which the coating layers are made. For example, thecoating layer may be made from a material which is transparent, even ifthe layer is relatively thick. The first coating layer and/or the secondcoating layer is thin enough such that the respective layer becomeslight transmitting while the material of which the layer is manufacturedis not transparent or translucent when manufactured in relatively thicklayers. The materials described herein are all transmissive for(visible) light or can be made in suitable layer thicknesses that aretransmissive for (visible) light.

A lighting device comprising a light source configured to generate lightsource radiation, especially one or more of blue and UV, and awavelength converter comprising the luminescent material as describedherein, wherein the wavelength converter is configured to convert atleast part of the light source radiation into wavelength converter light(such as one or more of green, yellow, orange and red light). Thewavelength converter is especially radiationally coupled to the lightsource. The term “radiationally coupled” especially means that the lightsource and the luminescent material are associated with each other sothat at least part of the radiation emitted by the light source isreceived by the luminescent material (and at least partly converted intoluminescence). Hence, the luminescent cores of the particles can beexcited by the light source radiation providing luminescence of theluminescent material in the core. In an embodiment, the wavelengthconverter comprises a matrix (material) comprising the luminescentmaterial (particles). For instance, the matrix (material) may compriseone or more materials selected from the group consisting of atransmissive organic material support, such as selected from the groupconsisting of PE (polyethylene), PP (polypropylene), PEN (polyethylenenapthalate), PC (polycarbonate), polymethylacrylate (PMA),polymethylmethacrylate (PMMA) (Plexiglas or Perspex), cellulose acetatebutyrate (CAB), silicone, polyvinylchloride (PVC), polyethyleneterephthalate (PET), (PETG) (glycol modified polyethyleneterephthalate), PDMS (polydimethylsiloxane), and COC (cyclo olefincopolymer). Alternatively or additionally, the matrix (material) maycomprise an epoxy resin.

The lighting device may be part of or may be applied in e.g. officelighting systems, household application systems, shop lighting systems,home lighting systems, accent lighting systems, spot lighting systems,theater lighting systems, fiber-optics application systems, projectionsystems, self-lit display systems, pixelated display systems, segmenteddisplay systems, warning sign systems, medical lighting applicationsystems, indicator sign systems, decorative lighting systems, portablesystems, automotive applications, green house lighting systems,horticulture lighting, or LCD backlighting.

As indicated above, the lighting unit may be used as backlighting unitin an LCD display device. Hence, the invention provides also a LCDdisplay device comprising the lighting unit as defined herein,configured as backlighting unit. The invention also provides in afurther aspect a liquid crystal display device comprising a backlighting unit, wherein the back lighting unit comprises one or morelighting devices as defined herein.

Especially, the light source is a light source that during operationemits (light source radiation) at least light at a wavelength selectedfrom the range of 200-490 nm, especially a light source that duringoperation emits at least light at wavelength selected from the range of400-490 nm, even more especially in the range of 440-490 nm. This lightmay partially be used by the wavelength converter nanoparticles (seefurther also below). Hence, in a specific embodiment, the light sourceis configured to generate blue light. In a specific embodiment, thelight source comprises a solid state LED light source (such as a LED orlaser diode). The term “light source” may also relate to a plurality oflight sources, such as 2-20 (solid state) LED light sources. Hence, theterm LED may also refer to a plurality of LEDs. The term white lightherein, is known to the person skilled in the art. It especially relatesto light having a correlated color temperature (CCT) between about 2000and 20000 K, especially 2700-20000 K, for general lighting especially inthe range of about 2700 K and 6500 K, and for backlighting purposesespecially in the range of about 7000 K and 20000 K, and especiallywithin about 15 SDCM (standard deviation of color matching) from the BBL(black body locus), especially within about 10 SDCM from the BBL, evenmore especially within about 5 SDCM from the BBL. In an embodiment, thelight source may also provide light source radiation having a correlatedcolor temperature (CCT) between about 5000 and 20000 K, e.g. directphosphor converted LEDs (blue light emitting diode with thin layer ofphosphor for e.g. obtaining of 10000 K). Hence, in a specific embodimentthe light source is configured to provide light source radiation with acorrelated color temperature in the range of 5000-20000 K, even moreespecially in the range of 6000-20000 K, such as 8000-20000 K. Anadvantage of the relative high color temperature may be that there maybe a relative high blue component in the light source radiation.

FIG. 4 schematically depicts a lighting device 20 comprising a lightsource 10 configured to generate light source radiation 11, especiallyone or more of blue and UV, as well as a wavelength converter 30comprising the luminescent material 1 with particles as defined herein.The wavelength converter 30 may e.g. comprise a matrix, such as asilicone or organic polymer matrix, with the coated particles embeddedtherein. The wavelength converter 30 is configured to (wavelength)convert at least part of the light source radiation 11 into wavelengthconverter light 21, which at least comprises wavelength converter light31 and optionally also light source radiation 11. The wavelengthconverter light 31 at least includes luminescence from the hereindescribed coated particles. However, the wavelength converter 30 mayoptionally include also one or more other luminescent materials. Thewavelength converter 30, or more especially the luminescent material 1,may be arranged at a non-zero distance d3, such as at a distance of0.1-100 mm. However, optionally the distance may be zero, such as e.g.when the luminescent material is embedded in a dome on a LED die. Thedistance d3 is the shortest distance between a light emitting surface ofthe light source, such as a LED die, and the wavelength converter 30,more especially the luminescent material 1.

FIG. 5a schematically depicts luminescent powder particles having asol-gel first coating forming a static powder bed during ALD of a secondcoating. The particles are indicated with references 100 and the sol-gelcoating or first coating layer is indicated with reference 110. Theluminescent cores are indicated with reference 102, and may include e.g.micrometer dimensional particles of a luminescent nitride or sulfidephosphor, but may also include other (smaller) material such asluminescent nanoparticles (see further FIG. 5c ). As schematically shownin FIG. 5a , the outer shape of the first coating layer 110 may have asomewhat pocked shape, as was found in SEM. By way of example, thesmaller particles in FIG. 5a indicate e.g. ALD precursor (see furtherbelow). Reference 100 a is used to indicate the luminescent particles100 only having the sol-gel first coating layer 110.

FIGS. 5b-5d schematically depict some further aspects of the particulateluminescent material; FIG. 5b shows a luminescent material 1, here byway of example two particles with luminescent cores 102, and a firstcoating layer 110 (formed by sol-gel coating), having a thickness d1,and a second coating layer 120 (formed by ALD), having a thickness d2.The thicknesses are not necessarily on scale. The possible indentationsin the first coating layer 110 are not depicted. The thickness d1 mayespecially be a mean thickness, averaged over the first coating layer110; likewise this may apply to the second thickness d2, etc. (see alsobelow).

FIG. 5c schematically depicts a luminescent core 102 which includes aluminescent nanoparticle, here by way of example a quantum dot 130. Thequantum dot in this example comprises a quantum rod with a(semiconductor) core material 106, such as ZnSe, and a shell 107, suchas ZnS. Of course, other luminescent nanoparticles may also be used.Such luminescent quantum dot 130 can also be provided with the hybridcoating.

As indicated above, the coating layer may include multi-layers;especially the second coating layer 120 may include a multi-layercoating. This is schematically shown in FIG. 5d , wherein the secondcoating layer 120 comprises an ALD multi-layer 1120, with layers 1121.References 1121 a, 1121 b and 1121 c schematically indicate theindividual layers, which may e.g. alternating Al₂O₃ layers (by way ofexample 1121 b) and Ta₂O₅ layers (by way of example 1121 a, 1121 c),respectively. Reference d2 indicates the thickness of the entire secondcoating layer 120. The individual ALD layers may e.g. have thicknessesin the range of 0.5-20 nm.

FIG. 5d indicates with references 17, 27, 37, 47 and 57 the surfaces ofthe respective layers. As indicated above, the layer thicknessesdescribed herein are especially average layer thicknesses. Especially atleast 50%, even more especially at least 80%, of the area of therespective layers have such indicated layer thickness. Hence, referringto the thickness d2 between surface 17 and surface 47, below at least50%> of surface 17, a layer thickness in the range of e.g. 5-250 nm maybe found, with the other less than at least 50% of the surface area 17e.g. smaller or larger thicknesses may be found, but in average d2 ofthe second coating (multi-)layer 120 is in the indicated range of 5-250.Likewise, this may apply to the other herein indicated thicknesses. Forinstance, referring to the thickness d1 between surface 47 and surface57, this thickness may over at least 50% of the area of 47 be in therange of 20-500 nm, with the other less than at least 50% of the surfacearea 47 e.g. smaller or larger thicknesses may be found, but in averaged1 of the first layer 110 is in the indicated range of 5-500 nm, such asespecially 20-500.

FIGS. 5a-5d schematically depict luminescent particles 100 having asingle nucleus. However, optionally also aggregates encapsulated withthe first and the second coating layer may be formed. This mayespecially apply for quantum dots as luminescent cores.

FIG. 6a shows the relative light output as a function of degradationtime (in hours) for phosphor powder before (SiO₂ only) and after ALDcoating (Al₂O₃ on SiO₂); degradation conditions: 60° C./100% relativehumidity: ALD-1: 20 nm Al₂O₃ on phosphor; ALD-2: 40 nm Al₂O₃ onphosphor; ALD-3: 20 nm Al₂O₃ deposited on SiO₂ coating; SiO₂−1: sol-gelSiO₂ coating on phosphor (basis of ALD-3). It is clear that only sol-gelcoated material or only ALD coated material is inferior to the hybridcoating.

FIG. 6b shows the relative light output as a function of degradationtime given in hours (85° C./100% RH); ALD-3: 20 nm Al₂O₃ on SiO₂coating; ALD-4: 20 nm Al₂O₃/Ta₂O₅ nanolaminate; deposited on thin SiO₂layer (<10 nm); ALD-5: 20 nm Al₂O₃/Ta₂O₅ nanolaminate; deposited on SiO₂coating; ALD-6: 20 nm Al₂O₃/HfO₂ nanolaminate; deposited on SiO₂coating. Amongst others, from these drawings can be concluded that ALDmulti-layers of Al₂O₃ and a second oxide provide superior behavior overa “simple” Al₂O₃ ALD coating. The ALD-3 sample in FIG. 6a is the same asin FIG. 6b ; the measurement conditions (temperature) were howeverdifferent.

FIG. 6c shows the relative light output (LO) as a function ofdegradation time given in hours (85° C./100% RH); ALD-3 and ALD-6samples as described above; ALD-7 with 20 nm Al₂O₃/HfO₂ nanolaminate onthin SiO₂ layer (<10 nm) (nanolaminate design: 4× [1.5 nm Al₂O₃/3.5 nmHfO₂]) and ALD-8 with 10 nm Al₂O₃/HfO₂ nanolaminate on thin SiO₂ layer(<10 nm), nanolaminate design: 2× [1.5 nm Al₂O₃/3.5 nm HfO₂]. It isclear that thicker sol-gel layers and/or more stacked nanolaminatesprovide better results than those with a thin sol-gel layer or amulti-layer stack with only a few layers. ALD-5 and ALD-6 have sol-gelcoatings in the range of about 100-200 nm.

Although particular implementations have been disclosed, theseimplementations are only examples and should not be taken aslimitations. Various adaptations and combinations of features of theimplementations disclosed are within the scope of the following claims.

Having described the embodiments in detail, those skilled in the artwill appreciate that, given the present description, modifications maybe made to the embodiments described herein without departing from thespirit of the inventive concept. Therefore, it is not intended that thescope of the invention be limited to the specific embodimentsillustrated and described.

What is claimed is:
 1. A wavelength converting device, comprising: acomponent; a film disposed on the component and comprising luminescentparticles, the luminescent particles arranged in multiple layers andconfigured to absorb light of a first wavelength and in response emitlight of a second wavelength, the film comprising an inorganic coatingdisposed on the luminescent particles to bond the luminescent particlesto each other and the component.
 2. The wavelength converting device ofclaim 1, wherein the luminescent particles comprise nitride phosphorparticles.
 3. The wavelength converting device of claim 1, wherein theluminescent particles comprise garnet or sulfide phosphor particles. 4.The wavelength converting device of claim 1, wherein the luminescentparticles comprise quantum dots.
 5. The wavelength converting device ofclaim 1, wherein the luminescent particles comprise first particles of afirst material and second particles of a second material different fromthe first material.
 6. The wavelength converting device of claim 1,wherein the component is a transparent substrate.
 7. The wavelengthconverting device of claim 1, wherein the component is a light emittingdevice configured to emit the light of the first wavelength.
 8. Thewavelength converting device of claim 1, wherein the component is areflective or absorptive substrate comprising a gap that is covered byat least some of the luminescent particles.
 9. The wavelength convertingdevice of claim 1, wherein the component is a reflective or absorptivesubstrate comprising a recess within which the luminescent particles aredisposed.
 10. The wavelength converting device of claim 1, wherein theinorganic coating is at least one of an oxide, a nitride, carbide,arsenide, phosphide, fluoride, sulfide, selenide, telluride, a singleelement, metal, and tellurite glass.
 11. The wavelength convertingdevice of claim 10, wherein the inorganic coating is aluminum oxide. 12.The wavelength converting device of claim 1, wherein the inorganiccoating is disposed to surround individual ones of the luminescentparticles in a single layer having thickness from 3 Angstroms to 10microns.
 13. The wavelength converting device of claim 1, wherein theinorganic coating is disposed to surround individual ones of theluminescent particles with multiple layers of different materials. 14.The wavelength converting device of claim 1, wherein the film is porous,and the inorganic coating has a first index of refraction nearlymatching a second index of refraction of the luminescent particles. 15.The wavelength converting device of claim 5, wherein the inorganiccoating has a first index of refraction nearly matching a second indexof refraction of the first particles and lower than a third index ofrefraction of the second particles.
 16. The wavelength converting deviceof claim 1, wherein the luminescent particles are non-oxide, and theinorganic coating comprises multiple layers surrounding each of theluminescent particles including an outer layer and an intermediate oxidelayer between each of the luminescent particles and the outer layer, theintermediate oxide layer having a thickness from 50 to 300 nm and theouter layer having a thickness from 5 to 200 nm.
 17. The wavelengthconverting device of claim 1, wherein the outer layer comprises amultilayer with layers having different chemical compositions, and thethickness of intermediate oxide layer is larger than the thickness ofthe outer layer.
 18. A light emitting device, comprising: a lightemitting diode configured to emit light of a first wavelength; a filmdisposed on the light emitting diode and comprising luminescent quantumdots, the luminescent quantum dots arranged in multiple layers andconfigured to absorb light of the first wavelength and in response emitlight of a second wavelength, the film comprising an aluminum oxidecoating disposed on the luminescent quantum dots to bond the luminescentquantum dots to each other and the light emitting diode.
 19. An array ofwavelength converting devices, comprising: wavelength converting devicesarranged in a matrix, each of the devices comprising: a component; afilm disposed on the component and comprising luminescent particles, theluminescent particles arranged in multiple layers and configured toabsorb light of a first wavelength and in response emit light of asecond wavelength, the film comprising an inorganic coating disposed onthe luminescent particles to bond the luminescent particles to eachother and the component.
 20. The array of claim 19, wherein eachwavelength converting device is a microLED pixel.